[en] Highlights: • Microfibers are present worldwide in marine sediments and seawater • Microfibers represent the most important percentage of microplastics, up to 100 % • The most abundant color in microfibers is blue. • Microfibers ranged from 0 to 459681 items·km^{- 2} in seawater and from 3 to 40 items per 250 g DW in sediments. • Polypropylene is the main polymer in microfibers analyzed - Abstract: The objective of this review is to summarize information on microfibers in seawater and sediments from available scientific information. Microfibers were found in all reviewed documents. An heterogeneous approach is observed, with regard to sampling methodologies and units. Microfibers in sediments range from 1.4 to 40 items per 50 mL or 13.15 to 39.48 items per 250 g dry weight. In the case of water, microfibers values ranges from 0 to 450 items·m^{− 3} or from 503 to 459,681 items·km^{− 2}. Blue is the most common color in seawater and sediments, followed by transparent and black in the case of seawater, and black and colorful in sediments. Related with polymer type, polypropylene is the most common in water and sediments, followed by polyethylene in water and polyester in water and sediments. Some polymers were described only in water samples: high-density polyethylene, low-density polyethylene and cellophane, whilst only rayon was reported in sediments.