The principles of activation analysis as a method of trace element determination are discussed and applications of neutron activation analysis to environmental problems reviewed. Thermal and fast neutron activation analysis using nuclear reactors, accelerators and252Cf sources are considered and recent developments in y‐ray spectrometry such as Ge(Li) detectors, anticoincidence shielded Ge(Li) detectors and multidimensional NaI(Tl) spectrometers are outlined. The advantages and disadvantages and sources of error in neutron activation analysis for trace element determination are discussed with emphasis on problems associated with the analysis of environmental materials. Applications of neutron activation analysis to air pollution studies, marine and fresh‐water trace element measurements and to the problem of mercury pollution are reviewed.