Chapter 1 is a general and historical introduction to the field of atomic nitrogen research. Specific mention is made of the methods by which atomic nitrogen has been generated and detected, and examples of its reactions with (predominantly organic) substrates are included. The overall aim of the thesis, the generation of atomic nitrogen in solution by mild thermolysis or photolysis, is stated. This concerns bond breaking, mainly in nitrogen heterocycles. In Chapter 2, 1,2,4-dioxazolidines are investigated and discussed according to the overall aim. Competing 0-0 and N-X (X = nitrogen substituent) scissions are compared by selective derivatisation. The thermal and photochemical fragmentation of these dioxazolidines is described, and evidence for atomic nitrogen and nitrene formation is adduced. Chapter 3 considers the use of heteroaromatic <i>N</i>-imines as a means to the proposed goal. Attention is centred on benzo[c]cinnoline <i>N</i>-imine, and its selective derivatisation. Radicals produced during photochemical decomposition of benzo[c]cinnoline <i>N</i>-imine derivatives are detected both directly and indirectly by e.s.r. spectroscopy, and evidence for the spin-trapping of atomic nitrogen is presented. In Chapter 4, the <i>in situ</i> oxidation of urazoles is investigated by e.s.r. spectroscopy, and <i>in situ</i> cycloadditions of these oxidised species are performed. 7-Azabenzonorbornadienes and 7-azanorbornadienes are applied as potential sources of atomic nitrogen in Chapter 5. The generation of the corresponding radicals is investigated by e.s.r. spectroscopy.