There is an abundance of information on closed-shell compounds containing sulphur linked to nitrogen; much less, of course, is known about free radicals containing this moeity. This review describes the wide variety of these radicals, their remarkable stability, the characteristic values of their ESR parameters, their electronic structures and their potential applications.KEY WORDS Electron spin resonance spectroscopy Free radicals Sulphur-nitrogen-containing free radicals 14N hyperfine interactions 33S hyperfine interactions powder spectra