Passport

A passport is a personal identification document for travel issued by national governments to their citizens. This is used by others to establish your nationality and thus, the rights and privileges accorded to your nationality (e.g. your ability to work in a certain country without additional documents, avail of consular services whilst abroad, open bank accounts overseas).

Passports are usually complemented by visas, which are issued by the country the traveller intends to visit. These can be obtained through an embassy or consulate (or through a company to which they delegated the application reception), and sometimes at a border crossing; they are usually pasted or stamped onto one of the passport pages. A valid passport or visa do not guarantee entry into another country.

A passport can sometimes also be used as identification in your own country, which is especially handy if your country has no national ID card and drivers licenses are not accepted or you don't have one.

Historically, children often could be included on a parent's passport. Today, many countries require even babies to have their own passport. Even when not required, having a passport for your child is a good idea. For example, if a baby is on Mom's passport and Mom has to fly home for some reason, then she must take the baby with her. If the baby has their own passport, you have more options.

Children travelling with only one parent may require additional documentation. This documentation may be a court order granting that parent sole custody or a notarized document in which the other parent gives permission. There are often strict measures in place for many countries to prevent incidents in which one parent takes a child, without the other parent's permission or in defiance of a court order, to another country.

This article contains general guidelines, and shall not be seen as legal advice.

The cover page includes the word "passport" and the name of the issuing country in the native language(s) of the issuing country (and possibly a second language, such as English); a coat of arms or national symbol; and in the case of biometric passports, a special, universal symbol. The name of a trading bloc such as the European Union (perhaps in another language), Mercosur or CARICOM may appear above or below the country name in cases where the group of countries issues passports designed to a common standard. The inside cover and first page usually contain introductory text, such as a disclaimer that the passport is the property of the issuing government, and a written request for safe passage and assistance to the bearer in the event of an emergency.

The information page of the passport records basic information about the passport. It lists your given name and surname; a photo; date and place of birth; validity period; issuing authority, place of issue and issue date; and passport number. Today most passports include machine readable information and many countries demand passports of visitors to be machine readable for them to be granted certain types of visa.

Most of the remaining pages will be blank. This provides space for amendments (where the bearer country's issuing may place travel restrictions, change conditions for travel abroad, or amend the period of validity), visas from foreign embassies or consulates, and stamps from passport control officers on entry and exit from various countries visited. An increasing number of countries no longer stamp the passports of most visitors. Instead, the details of admission will be printed on a slip of paper (Hong Kong and Macau), sent to a traveller's email address on file (Singapore), or made viewable through a website (U.S. and Australia) or app. In some cases, a stamp can be given on request.

The European microstates Monaco, San Marino and Liechtenstein do not have immigration checks on their borders with the neighbouring countries, but tourists wanting a passport stamp can still obtain one by visiting the relevant government office.

A few pages of the passport may serve to provide helpful legal and practical information. E.g., the U.S. passport contains six pages of website URLs and contact information that addresses travel restrictions and concerns (treasury restrictions on imports, paying taxes while in a foreign country, registering your stay in a foreign country), common sense subjects (don't be a target, be mindful of security threats, ways to lose citizenship), instruction on obtaining consular assistance in an emergency and on reporting and replacing lost, stolen or damaged passports.

Only the information page and the booklet's physical dimensions are standardised by ICAO. The issuing nation or trading bloc is free to change any of the other content at will.

Avoid putting novelty stamps in your passport. Even though novelty stamps from some places such as Machu Pichu, Checkpoint Charlie, Churchill or various micronations are popular souvenirs, they are not official country stamps and may invalidate your passport.

Extra pages

Some destinations require there to be two blank pages in your passport before you enter the country. If you are running low on blank pages, some countries may issue a new passport "cross-linked", or even physically bound, to the old one. The old passport must have a blank page for the authority to endorse a cross-link. This is useful not only when a passport is running low on blank pages, but also in cases where the visa outlasts the passport that contains it.

Some countries used to offer the addition of extra pages to an existing passport (for free or a fee) at a passport office, embassy, or consulate. Due to ICAO's "write-once" policy on biometric passports, this option is not available for those who have biometric passports. The U.S. and UK no longer add extra pages to existing passports, but may offer the option of a 48 or 52-page booklet (instead of the standard 28 pages) when the passport is originally issued.

A second passport

It can be possible for a person to hold multiple passports from a single country at the same time, although not all countries allow this. Even for those countries where this is allowed, it is something of a rarity; not even all immigration officials know that this is possible and legal. If you are off the beaten track, it is advisable to only show the passport that is needed for that particular border, as multiple forms of the same ID can look suspicious.

Instances where second (or even third) passports can be issued include:

If there is little or no space left for new visas, but the current passport has valid visas that are still needed, both passports need to be valid simultaneously.
If you need to submit your passport to two or more embassies at the same time for visas, then you need two or more passports.
A representative of a national government (head of state, minister of government, ambassador or high commissioner) may be issued a special passport for journeys in that capacity. When not travelling on official government business, a separate standard passport is used.
Some countries (such as Libya and Iran) will not allow entry to people whose passports show evidence of travel to Israel, so a new passport may be necessary for travel to those countries. See Israel#Get in and Visa trouble for more information.
If a place is insisting that they require a passport as collateral (hotels, car rental), providing them the second passport not used for entry is the safer option. If they wrongfully withhold this passport, the damage done is reduced, as you still have the correct passport to clear immigration.

Types of passports issued

Regular (or tourist) passport

This is the most common type of passport issued to citizens for general international travel for both tourism and business.

Diplomatic passport

See also: Diplomatic missions

As the name implies, this passport is typically issued to senior diplomats and their immediate family members, as well as high-level government officials. Visa requirements are often different.

Official passport

This type of passport is generally issued to government employees, military personnel, and elected officials for work-related travel. These are often treated like diplomatic passports, although the covers will differ in color from standard or diplomatic passports.

Internal passport

In some countries, an internal passport is an identity document that often serves as a citizen's identity card. Only two countries issue internal passports: Russia and North Korea.

Citizens of Russia cannot be issued an internal passport at their local consulate or embassy; they must be physically present in the country to get it.

A Belarussian passport is unique in the sense that it serves as both an internal and external passport.

Passport cards and EDLs

The Western Hemisphere Travel Initiative, a U.S. law which since 2009 has required a valid passport or other approved secure document for even the most trivial "international" trips overland between the U.S. and adjacent points (such as Canada, Mexico, Bermuda and the Caribbean), has been accompanied by a flood of specialized identity cards and trusted traveller programs. These cards do not comply with ICAO standards; they are intended as passport alternatives for travel to adjacent countries by land or sea. They are not usable for air travel.

If you live on CanUSA Street in tiny Beebe Plain, Vermont these cards will let you leave your driveway. (The road, Québec Route 247, is in Canada.)

Likewise, a Border Crossing Card issued by the U.S. government to a few trusted travellers in Mexico substitutes for both a passport card and a tourist (B2) visa.

Along the Canada-U.S. border, a few states (Michigan, New York, Vermont, and Washington) and provinces (British Columbia, Manitoba) issue an enhanced driver's license (EDL). U.S. authorities accept the card as functionally the same as a passport card, routinely accepted for re-entry into the U.S. by land or sea. Canadian authorities regard an EDL as proof of identity, but not proof of nationality, so they should be used along with a birth certificate or another proof of citizenship.

The U.S. passport card has identical requirements to the passport book, but is issued in card form for convenience. It is cheaper than a passport book (only $35), but otherwise no easier to obtain. It can be used as proof of citizenship, and for entry at land borders and seaports of WHTI countries. The Passport card cannot be used for international air travel.

U.S. state-issued enhanced driver's licenses often cost more than the $30 passport card for a validity period that is half or less. In addition, you might forfeit any existing time on your existing driver's license, and you're left with just one form of ID, instead of two. Even if a regular U.S. passport book has expired, you have five years to apply without extra fees for verification.

Canada does not issue a "passport card". Canadian passport renewals are possible if the passport expired less than a year ago, but incur the same onerous fees as a new passport ($190/5yrs or $260/10yrs, plus the photo).

If you lose your wallet, a couple of forms of alternate identification are often needed to get your driver's licence and other cards replaced. An ICAO-style standard passport, because it's separate from your other documents, is invaluable in this case.

Irish citizens may also avail of a Passport card in addition to a Passport booklet - unlike the US Passport card, the Irish Passport card is valid for air travel within the European Union and EEA and to Great Britain. At passport control, the Irish Passport card functions to all intents and purposes in the same way as an ID card issued by an EU member state.

Identity cards

Most European countries have some form of government-issued ID that is often mandatory to possess for every citizen above a certain age and is accepted in lieu of a passport when crossing some international borders. Within the Schengen area, this type of ID is all you need to legally cross borders, even though some airlines might think otherwise. Citizens of EEA countries can also use this ID card to enter countries on the Balkan Peninsula and Turkey (from the West, not from Iran, Iraq, Syria), despite the fact that they are not part of the EU.

Most countries in South America are members of the Mercosur organization. Citizens of such countries can travel to other Mercosur countries with just their national ID card.

The Central American countries of El Salvador, Honduras, Nicaragua, and Guatemala also allow their citizens to move freely between those countries with just a national government-issued ID card. The agreement establishing this zone of free movement further stipulates that citizens of third countries don't get charged or their passport stamped upon crossing a border between for example Honduras and El Salvador. However, the actual enforcement of this rule may very well depend on the mood of border officials.

Hong Kong permanent residents can use their identity card to enter Macau, and vice versa.

Other permits

To enter mainland China, citizens of Hong Kong and Macau, are required to apply for a Home Return Permit (回鄉證/回乡证). The Chinese government does not allow them to enter using their passports. Likewise, a mainland Chinese passport is not accepted for entry into Hong Kong and Macau; mainland Chinese citizens need to obtain an Exit-Entry Permit for Travelling to and from Hong Kong and Macau (往来港澳通行证).

Taiwanese passports are not accepted for entry into mainland China due to the Chinese government's non-recognition of Taiwan as an independent country. Instead, Taiwanese citizens need to apply for a Taiwan Compatriot Pass (臺胞證/台胞证) from the Chinese government. Likewise, Chinese passports are not accepted for entry to Taiwan, and mainland Chinese citizens instead need to apply for a Taiwan Entry Permit (入臺證/入台证) from the Taiwanese government.

Temporary or emergency passports

If your passport is lost or stolen, it may take considerable time to issue a replacement — for example, Canadian missions typically require at least 20 working days after you give them the application with all required documentation. This can be seriously inconvenient if you are abroad, especially if you have onward travel planned or if you also have to go to local authorities to replace the visa which was in the lost passport.

Many missions can also issue a temporary or emergency passport. For some countries, only one is available; for others, they are two different documents. This is much faster, e.g. for Canada three working days. Some restrictions apply to these passports. An emergency passport is usually good for only one journey and a temporary one only for a few months. Also, some countries may have different visa requirements for them; for example the Philippines provides a visa-on-arrival for holders of many passports, but anyone with an emergency or temporary passport from any country must obtain a visa in advance. Airlines will refuse to fly you without it.

Certificate of identity

A refugee or stateless person cannot obtain a passport. Under the 1951 Convention Relating to the Status of Refugees, these persons may obtain a passport-like booklet bearing the words "Travel Document" from the country in which they've taken refuge. Historically, the UN High Commission on Refugees issued documents which served a similar purpose to the individual-nation "re-entry permit" or "Certificate of Identity". As none of these confer citizenship, most countries will not allow visa-free or visa-on-arrival travel to people using these.

In Hong Kong, new immigrants who haven't become permanent residents can apply for the Document of Identity for Visa Purposes which works essentially the same as normal passports. However, document of identity holders enjoy much less visa-free privilege.

Meanwhile, Taiwanese travellers who wish to visit places which deny holders of Taiwanese passports, or simply inconvenient to apply for a Taiwan Compatriot Pass for a visit to China can also apply for a Travel Document (中华人民共和国旅行证) issued by Chinese (PRC) foreign embassies or consulates, which won't affect their Taiwanese citizenship. However, airlines and other businesses may not be familiar with Chinese travel documents, so you should prepare for explanation.

The United Nations and Interpol issue passport-like documents to a limited number of their own officials. The willingness of individual countries to accept these as stand-alone travel documents (instead of requiring they be used with a national passport) varies.

Technology and security

Some countries require certain security features on passports to issue *on-the-spot* visas (visa on arrival), biometric and machine readable passports are the most common requirements. The OCR text appears on the identification page.

Over the years, the way passports are produced have changed. Passports with handwritten information pages still exist, although they are being phased out due to security concerns.

Beginning in the 1990s, machine-readable passports have been gradually introduced. In them the personal data is encoded into two strips at the bottom of the page, allowing it to be read automatically. This helps speed up queues at most passport control stations, as there is less for officers to manually type into the computers.

Most nations have implemented biometric passports, containing an RFID (radio frequency identification device) chip which contains (depending on issuing country) an electronic recording of passport data, a photograph, and/or fingerprints. Consequently, personal appearance at a designated application centre (including a post office) has become mandatory. Basically, an RFID station issues a signal, and the RFID chip responds with some or all of its data. They are highly useful for customs and immigration officials to more quickly and accurately identify and process you. However, these chips can be read by others as well; the equipment typically has a range of about a metre and is moderately priced, widely available and easily concealed. This creates several security problems:

tracking by intrusive governments
tracking by merchants or con artists who target certain nationals
identity theft where the thief starts with all the information on your passport

If concerned, you might:

inquire of the issuer as to the RFID security measures. Some passports, e.g. Swiss ones, don't respond to any signals when closed.
do Internet research to understand the issues.
choose to use a passport wallet that confines the RFID signals until you deliberately remove your passport for inspection by officials. Such wallets are available at moderate cost from better travel accessory merchants. Many of the "geek" clothing sites on the web also have them.

Where and how to apply

Your home country's passport issuing authority will most often be part of the ministry of foreign affairs (the State Department for the U.S.) or the ministry controlling the border guards, immigration, national police, or registration of person (HM Passport Office is part of the UK Home Office). Applicants may go to their nearest representative or satellite office or third-party intermediary authorised to receive applications on their behalf. In this case, applicants need to visit the website of the passport issuing authority for more details.

In some countries, applications can be initiated online. In some cases, you will be required to print, sign, and submit the application form you filled in online, while in other instances the form will be directly submitted to the issuing authority for processing.
Regardless of the issuing authority, in many countries passports are physically issued by major police stations or local city council offices.
In some countries, post offices have application forms and instructions.
Passport offices operate in the largest cities; it may be possible to apply in person or by mail.
If there's nothing available locally in your region, the office of your elected representative to national government sometimes may offer assistance.
If you are abroad, you can go to your home country's embassy or consulate to apply. This sometimes involves longer issuing times and higher fees given the need to transport them to and from a single processing centre in the issuing country.

To obtain your first passport, you will have to provide documentation with your application proving your identity and claim to citizenship. There will likely be a fee; the issuing government may also require the signature of one or more guarantors (specific national requirements vary, but this person must be a fellow citizen who knew you for some minimum length of time — often a couple of years — and may be required to hold a passport, a professional license or some other easily-verified credential).

Personal appearance is increasingly mandatory given the requirement to collect biometric identifiers from the applicant and verify the applicant's identity. In some cases you will be required to book an appointment and the application centre may not accept mere walk-ins to manage security, workloads, and processing times.

A recent, clear, head-and-shoulders color photo in some specific size and format is needed. Often they want two copies, one to be mounted and embossed in the finished document by the passport issuing center, and one for their files. There may be additional requirements such as having a neutral expression and looking at the camera (not easy for a baby), having the photographer indicate their name in addition to the place and date the photo was taken, or having a guarantor sign the photo to indicate that it shows the applicant. Some countries, on the other hand, do not allow you to bring your own photos. To ensure authenticity and best quality, photos will be taken on the spot by the employee processing your application.

Passport photos can be taken at some passport application centers (for example, the United States Postal Service and Post Office in the UK receive passport applications and offer passport photos for citizens in their respective countries). Passport photos can also be taken at photo studios, some other businesses, and some self-service photo booths (if they meet the technical requirements). Automobile associations often offer photos to their members at a slight discount. There are also smartphone apps that let users take passport photos at home, but not all countries accept these. In some cases the photos taken at application centres are in addition to the ones provided by the applicant and it will be up to the passport issuing authority which one to use in the passport.

If you are getting passport photos taken from a third party provider, consider having a few extra printed since some countries require them for visa applications (though check for how recent those photos need to be). Photos can be painfully expensive in many countries. In some countries, though (particularly in Africa or Asia) they cost very little. Requirements on photo size and age of the photo may differ across countries and between passports and visa applications. Check requirements to be able to carry the needed photos, and some extra.

Once you have a passport, many nations can use it to substantiate your identity when you apply for a new one, i.e. documentary requirements to prove your identity and citizenship will be much less. Each application must be accompanied by one or more photos, more or less similar to your first passport. Lastly, as noted by Erma Bombeck in 1991, "when you look like your passport photo it's time to go home".

What if I lose it while travelling?

See also: Theft#Passport and identity theft

Some people have experienced the nightmare of losing their passport. If this happens, take a deep breath and contact your embassy or consulate immediately to begin the replacement process. It can take anywhere from a few days to several weeks to get a new passport in a foreign country, depending on your citizenship and your location.

Some countries offer "emergency passports" or "emergency travel documents" if you can convince them that you can't wait out the normal turnaround time (see above). These documents usually have a very short-term validity, typically only being good for one journey to your home country, although some may be valid longer. They take much less time to obtain than a full-blown replacement passport — often just hours. The process can be expedited by having a copy of the original, as discussed below. A police report is useful and may even be required by your embassy/consulate, even if there was no crime involved. Don't forget to bring a couple of passport photos.

Make copies

Seasoned travellers often carry multiple photocopies of their passport (and other important documents, such as visas) when abroad. You should keep copies in locations separate from the originals, e.g. folded together in your wallet, in your luggage, or even scanned into a computer.

This is especially useful when travelling in areas where risk of loss or theft is high. Lacking an original, a copy could save you from problems with local authorities by quickly showing them something that indicates you are authorized to be there — before they arrest you.
Copies also may make a replacement passport easier to obtain through your embassy or consulate so you can return home. You should also make or get a copy of any entry visa required to enter a country.

Use original passports when demanded by authorities, such as when checking in for a flight, at immigration as you reach another country, or for cruise ship embarkation processing.

If afoot, with your passport elsewhere (e.g. at your hotel), a copy and government-issued photo identification are decent substitutes that give authorities reason to check your hotel before official action.
If cruising, unless the ship's staff states that passports are necessary for a port visit, leave them in your cabin's safe and take the copies and ID instead.

Copies are best done in color, and at least of the primary page(s) of each original. Two adjacent pages of two passports can often fit on a single sheet of copy paper.

Giving your passport to others

In some countries, such as China, it may be necessary for your long-term residence or immigration status to be registered with the local police. It is advisable to give your passport to a trusted agent if you will not do this in person. Often the employer will have a staff member handle this.

Some countries require hotels to keep photocopies of your passport, both the photo and the visa page. It is not clear whether they are required to check the visa and call police if it is expired, but certainly some will refuse a room if your visa is not correct. If you don't trust hotel staff with your passport, for instance if staff have to leave the hotel premises to make a copy, you can provide your own photocopies.

Under international law it is quite legal for anyone you do business with to ask to see a passport as positive ID, and even to keep a photocopy for their records - how they use the data found on that passport will be subject to data privacy or data protection laws of the country they are in. However it is not legal to ask anyone to surrender a passport for any purpose except visa processing by the host government, things your consulate might do like renewing your passport or issuing one for your child, or when ordered to by a court of law (e.g. when the passport holder is subject to legal proceedings and is granted bail). Not "for safe keeping" or as any sort of "security guarantee". If your passport is taken for any such reason, contact your embassy or consulate; they can demand that the host government get it back for you and, at least in theory, that government is obligated to do so; typically they will contact local police who will in turn contact whoever has the passport. However, while international law is absolutely clear on this, it may not work in all countries.

Expiry dates

	Note: Many countries require six months validity for your passport, even if you have return tickets well ahead from the expiry date.

The expiry date on your passport is the last day it can be accepted as proof of your identity to obtain key services within your home country (e.g. opening a bank account, voting). For travel however, the last date when you can use a passport is well before the expiration date. As you start international travel, most immigration authorities and transport companies (such as airlines or cruise lines) will demand that your passport have sufficient time before it expires, which is typically six months. They are helping to ensure that you will meet immigration requirements of the countries you'll visit: these often include having three or six months of validity left on your passport; depending on the country you are entering, you may be required to have it upon your arrival (i.e. your passport should expire no sooner than three or six months after you enter the country) or on your expected departing date. In the latter case, your passport should expire no sooner than three or six months after you plan to leave the country (to this respect, you are usually also required to submit proof of your outbound trip, such as an international airline ticket); this is the case, for example, when requesting a Chinese visa. You may have to stay longer than planned, for instance due to serious injury or illness. Overstaying your visa or holding an expired passport without any pending renewal application could have serious consequences.

If your passport does not have sufficient time before expiring, then you may be denied boarding or entry into a foreign country. If remaining validity is a requisite for obtaining an entry visa, you are likely to be denied.

Passports from many countries (Australia, most EU nations, the U.S.) remain valid for ten years. Others allow shorter validity, such as Sweden (five years) and Belgium (seven years). For some countries, such as Canada, it depends on the passport type; older passports were only good for five years but the new RFID ones are good for ten. In many countries the period of validity depends on age; even if adults get ten-year passports, children may get only five. You may also get a passport only for a limited duration when the required age for military conscription is nearing. Some countries don't accept old passports; a passport may be regarded as expired after ten years regardless of its expiry date.

All passports will eventually expire, and depending on your country it can take anywhere from one day to four months or longer to issue a new one; order your passport well ahead of your intended trip. Some countries offer a faster delivery of the new passport for a higher fee than the normal one.

In some countries, particularly the United States and the United Kingdom, a multiple-entry visa affixed on an expired passport remains valid until its expiry date, and you should bring both the expired passport (with the visa) and your new passport, if you still wish to use the visa.

Other restrictions

See also: Visa trouble

Citizens of many countries may not have legal or constitutional rights to be issued a passport by their country of citizenship. The passport can thus be denied. Those convicted of certain illegal drug and sex crimes may be ineligible, especially if they're on probation or parole. Also, those who owe money for taxes, child support, etc. Even if no law was broken, service in the military or government of a foreign nation may cause ineligibility, especially if you were a non-citizen where you served. On the other hand, if you immigrated to another country and later became a citizen, prior service would rarely be a problem to obtaining a passport of your new nationality.

In some countries, travellers may be required to surrender their passport to local authorities at certain times, such as when they are subject to criminal proceedings (for example, this can be one of the conditions for being released on bail, to ensure that the traveller is not a flight risk). An exit visa is required to leave some countries and that may be denied for various reasons.

In some cases, countries with poor or no diplomatic relations with another country may bar the bearers of the other country's passport (or merely having stamps of that other country) from seeking entry.

Israel

Israeli passport holders, as well as anyone with an Israeli entry/exit stamp in their passport (or even any other proof of having been to Israel), will face restrictions and possibly be denied entry to many Arab or Muslim states. Similarly, entry into Israel with a passport from an Arab or Muslim state (or stamps from them) can cause long delays and possibly denial of entry.

Cuba

See also: Americans in Cuba

U.S. citizens who do not get special permission from the U.S. State Department to visit Cuba have a similar problem: for a U.S. citizen to spend money in Cuba without permission from the Treasury Department is a punishable crime, and any visit is presumed to involve expenditures of money. Cuban authorities, too, will stamp a separate piece of paper, if so requested. However, multiple entry stamps to third countries like Mexico could be a red flag.

North Korea

U.S. and South Korean citizens face restrictions by their respective governments from visiting North Korea. They may travel there only for approved reasons and must seek a special permit to do so from the relevant government agency.

Multiple citizenship

Multiple citizenship can cause some trouble. On one hand you may have obligations that don't get enforced as long as you don't enter the country where they apply, on the other hand you may need to "pose" as a citizen of the right country during your travel – and which one is right varies.

Multiple citizenship may be especially problematic in countries that don't recognise it, and in cases where you got a non-renounceable citizenship "by accident", such as travelling to the United States just to be born, or (as a woman) marrying an immigrant from Iran.

In many countries, you are legally required to use the passport you used to enter the country to exit from it. In most, it may cause practical difficulties, such as being accused of overstaying, if you don't.
Equally challenging: when flying into a country, if possible you should use on entry the passport you used to check in for the flight.
Once you've entered a country, you should generally keep using whatever passport you used to enter it for the whole time you're there. (The obvious exception is that you might want to use a different passport to check in for your flight out.)
In some countries, such as Australia, Colombia, South Africa and the United States, you are legally required to use that country's passport to enter and exit the country if you are a citizen of it, even if you hold multiple citizenships.
Some countries do not recognize multiple citizenship; therefore, being found in possession of another country's passport may cause you legal problems. Penalties could include stripping you of the citizenship of the country that you are in. You must also ensure that you enter the country with the passport of that country or risk being accused of entering illegally.
Multiple citizenship does not exempt you from legal responsibilities such as military conscription or paying taxes in the countries of your nationalities – and serving in a foreign military is also grounds for loss of citizenship in many countries. There is often an exception for conscription, and agreements to avoid double taxation, but there is no general guarantee for such exceptions to apply.
It is very unlikely that consular assistance is available from any of your other countries if you need help in a country where you are a citizen. Often a prisoner can ask to be transferred to their own country, but this option may not be available for you.
If you have multiple citizenship, you may find yourself wanting to leave a country on one passport and then enter another country on a different passport, for instance to avoid visa fees. If you want to do this at a land border crossing, contact a consulate beforehand, in writing, to ask if it will be all right. Even if they say it'll be okay, the second country's border control may be confused by your lack of an exit stamp – if so, explain your situation; they may ask to see your other passport, but they have surely seen dual citizens before. In some countries, border officials may insist on you using the same passport on both sides of the border, so it really is important to ask first and get the answer in writing. When traveling by air, this is not typically a problem.

Exit visa or stamp

The countries of the Gulf Cooperation Council (Saudi Arabia, Bahrain, Kuwait, Oman, Qatar, and the United Arab Emirates) require foreigners on certain classes of visas to obtain exit visas in order to leave the country. The most notable example is those on work visas, who are required to obtain permission from their employer in order to leave the country.