A lunar base will go through evolutionary development, starting with limited capacity and expanding over time. Lunar development will stage in three main phases. In each of these phases a different generation of habitats will necessarily evolve.

1st generation: Prefabricated and pre-outfitted hard shell modules.
2nd generation: Assembly of components fabricated on Earth with some on-site assembly required.
3rd generation: Large structures comprised substantially of local materials.

Since 1st generation concepts are already well understood and 3rd generation facilities are still far off, highly complex, and can only be based on many assumptions, our main focus is on second generation - mainly prefabricated - lunar bases.