Present information about the principal processes in the radiolysis of polyphenyl hydrocarbons is summarized and interpreted. These processes are considered to be: (1) the dissociation of energized aromatic molecules into radicals and molecular products; (2) the interaction of aryl radicals with aromatic hydrocarbons and themselves; (3) the interaction of hydrogen atoms with aromatic hydrocarbons; (4) product formation by processes not involving hydrogen atoms or other radicals. The processes leading to the formation of “polymer” and the composition of this “polymer” are described. Finally the effects on hydrogen yield and “polymer” yield of temperature change, phase change, and change of radiation type (the linear energy transfer effect) are interpreted.