Exploration of the Moon is the most crucial and decisive step toward human expansion into the vast reaches of space. The Moon is the natural and ideal testbed for determining human capability to survive, function, expand and settle into the space environment. Scientific studies, astronomic observations, and exploitation and utilization of space resources culminating in the establishment of a self-sufficient permanently human-tended lunar base are the goals of lunar exploration. Four development stages in the evolutionary exploration of the Moon are suggested: (1) exploratory; (2) pioneering; (3) outpost; and (4) base. Overall goals and specific objectives, functional requirements, construction conditions, and life support systems requirements needed in each stage are identified.