The geology of the planets bears directly on three basic aims of lunar and planetary exploration: determination of the origin and evolution of the solor system; determination of the origin and evolution of life; and clarification of the nature of the processes shaping man's terrestrial environment (National Academy of
Sciences, 1966 ). The purpose of this report is to suggest guides to the orderly geologic exploration of the planets and the assignment of priorities to specific experiments and to indicate where supporting Earth-based research can be most profitably pursued. The kinds of data that are most relevant to geologic interpretation are specified, and the sequence in which these data should be acquired is outlined. The report does not provide detailed consideration of the
engineering problems involved in acquiring the data, but the exploration suggested appears practical in view of present flight plans and probable future flight opportunities.