"Nitrogen" SuppL. Vol. 82 continues the description of binary compounds composed of nitrogen and hydrogen (nitrogen hydrides). While" Nitrogen" SuppL. Vol. 81 covers mono- nitrogen compounds, the present volume comprises compounds having two, three, four, or more nitrogen atoms. Hydrazine, N H , and its ions N2Ht and N2H~+ were not included. 2 4 (Reference is made to a voluminous monograph: E.W. Schmidt, Hydrazine and its Deriva- tives: Preparation, Properties, Applications, Chichester 1984, 1088 pages.) Among the dinitrogen compounds, the diazenyl cation, N H+, has been extensively inves- 2 tigated, especially in regards to spectroscopic and kinetic properties, because of its occur- rence in interstellar space. Chemically well-characterized are diazene, N H , the simplest 2 2 unsaturated nitrogen hydride which is used as a hydrogenation reagent, and the hydrazyl radical, N H , which is frequently present as an intermediate during the formation and 2 3 decay of nitrogen-hydrogen compounds. The major portion of this volume is taken up by hydrogen azide or hydrazoic acid, HN , the first member in the series of trinitrogen compounds. Known to be highly explosive 3 in pure form, it can be safely handled when diluted. Thus, a great deal of information is available mainly on its properties as a chemical reagent and its decomposition processes.