A baseline ECLS system for a lunar base manned intermittently by four crewpersons and later permanently occupied by eight crewpersons has been designed. A summary of physical characteristics for the intermittently manned ECLS system includes a launch weight of 10,590 lb, launch volume of 955 ft3, 90-day resupply weight of 5972 lb, 90-day resupply volume of 346 ft3, and a power requirement of 10.494 kW. Evolution into a continuously manned base generates the following incremental requirements: launch weight of 19,935 lb, launch volume of 1178 ft3, 90-day resupply of 4928 lb, 90-day resupply of 403 ft3, and power requirement of 10.695 kW. A supplementary study assessed tankage requirements, penalties incurred by adding subsystem redundancy and by pressurizing large surface structures, and difficulties imposed by intermittent occupancy. Alternate concepts using lunar derived oxygen, the gravity field as a design aid, and a city utility type ECLS system offer potential advantages.