[en] The determination of mass fraction of elements at major to trace levels with high precision and accuracy is a challenge. Activation analysis techniques in general and NAA, PGNAA and CPAA in particular are suitable for such purposes. These techniques are applied to diverse samples in different fields including geology, life sciences, environmental sciences, archaeology, metallurgy, material sciences, agriculture, nuclear technology, and forensic sciences. In addition to total mass fraction, it is important to characterize isotopic composition and chemical speciation of elements. It is also important to develop newer methodologies in activation analysis to deal with complex matrix samples for various elements of interest and also to achieve improved sensitivities and detection limits compared to complementary nuclear/radioanalytical as well as conventional analytical techniques. International Conference on Modern Trends in Activation Analysis (MTAA) is conducted once in every 4 years, since its inception in 1961, to discuss recent developments and applications as well as future prospects of activation analysis. The MTAA conferences, in reverse chronological order, were held at: Bhabha Atomic Research Centre, Mumbai, India (MTAA-15, 2019), Delft University of Technology, Delft, The Netherlands (MTAA-14, 2015), Texas A&M University, College Station, USA (MTAA-13, 2011), Tokyo Metropolitan University, Hachioji, Japan (MTAA-12, 2007), University of Surrey, Guildford, UK(MTAA-11, 2004), National Institutes of Health in Bethesda, Maryland, USA (MTAA-10, 1999), Korea Atomic Energy Research Institute, Seoul, South Korea (MTAA-9, 1995), Technical University of Vienna Atominstitut, Vienna, Austria (MTAA-8, 1991), Riso National Laboratory, Copenhagen, Denmark (MTAA-7, 1986), University of Toronto, Toronto, Canada (MTAA-6, 1981), Technical University of Munich, Munich, Germany (MTAA-5, 1976), CNRS du Cyclotron, Saclay, France (MTAA-4, 1972), National Bureau of Standards, Maryland, USA (MTAA-3, 1968), Texas A&M University, College Station, USA (MTAA-2, 1965) and Texas A&M University, College Station, USA (MTAA-1, 1961). The MTAA-15 was the very first MTAA conference ever held in India and it was organized by Bhabha Atomic Research Centre (BARC) during November 17-22, 2019 at the Department of Atomic Energy (DAE) Convention Centre, Anushaktinagar, Mumbai-400094. It was organized in association with the International Committee on Activation Analysis (ICAA) and Indian Association of Nuclear Chemists & Allied Scientists (IANCAS) with partial funding from the Board of Research in Nuclear Sciences (BRNS), DAE, Government of India. The scope of MTAA-15 included areas such as Neutron activation analysis (NAA), Prompt gamma-ray NAA (PGNAA), Charged particle activation analysis (CPAA), Photon activation analysis (PAA), Fast neutron activation analysis (FNAA), k₀-based conventional & internal monostandard NAA & PGNAA, Preconcentration, radiochemical, chemical & speciation NAA, Research reactors, accelerators & other facilities for activation analysis, Instrumentation for activation analysis, Applications of activation analysis to various fields, Applications of activation products, Applications to reference materials & QA/QC in measurements, and Complementary radioanalytical techniques. (author)