A CELSS has been defined based on current or near-term technology. The CELSS was sized to support the metabolic load of four people on the Moon for ten years. A metabolic load of 14 MJ/person/day is assumed, including an average of 2.6 hr of EVA/person/day. Close to 100% closure of water, and oxygen, and 85% closure of the food loop is assumed. With 15% of the calories supplied from Earth, this should provide adequate dietary variety for the crew along with vitamin and mineral requirements. Other supply and waste removal requirements are addressed.The basic shell used is a Space Station Freedom 7.3 m (24 ft) module. This is assumed to be buried in regolith to provide protection from radiation, meteoroids, and thermal extremes. A solar dynamic power system is assumed, with a design life of 10 years delivering power at 368 kWh/kg. Initial estimates of size are that 73 m2 of plant growth area are required, giving a plant growth volume of about 73 m3. This assumes a mixture of crops achieving production rates equal to the best published data. With a volume of 108 m3 per module, other support equipment can be accommodated within one module. In particular, anaerobic and aerobic digestion is used to recycle inedible biomass. Automation is used to the extent necessary to keep manpower requirements in the range of 10% of the supported crew time. About 100 kW of electrical power is required, primarily driven by plant irradiance. Because of the cost of rejecting low-grade waste heat to the environment during the lunar day, sunlight is assumed to be used directly for plant irradiance when available.The goal of this design concept was to focus our thoughts. We believe it represents something that is achievable, although there are uncertainties in the data used to develop it. Among these uncertainties are the effects of fractional gravity and closure on plant growth and other biological processes, the need for appropriate automation and materials handling technologies, and the relative costs of infrastructure utilities (mass transportation, electricity, manpower, etc.).