Cyanamide, dicyandiamide, and the related cyclic azines (melamine, ammeline, ammelide, and cyanuric acid) were reacted in water at 100-300 degrees C in a sealed 316 SS tube (275 bar) for the purpose of characterizing the hydrothermolysis chemistry of cyanamide. The conversion of cyanamide to dicyandiamide dominates at 100-175 degrees C. At 175-250 degrees C, when the reaction times are shorter than 15 min, the major pathway is hydrolysis of the cyanamide-dicyandiamide mixture to CO2 and NH3. A minor pathway is cyclization to higher azines (melamine, ammeline, ammelide and cyanuric acid). Above about 225 degrees C, hydrolysis of these cyclic azines to aqueous NH3 and CO2 occurs in a relative ratio which depends on the particular cyclic azine, and, to an extent, which increases with temperature. At 300 degrees C the conversion of all compounds to CO2 and NH3 is complete in 10 min. The hydrothermolysis chemistry of cyanamide and urea are compared.