Abstract: A modular building system in which individual cuboid modules are assembled at a manufacturing facility, optimized for transportation, and transported to a building site by conventional delivery systems. On site, the modules may be modularly assembled into multi-modular buildings. Buildings may be assembled by attaching together a plurality of the structurally self-supporting modules. The modules may be attached horizontally adjacent or vertically adjacent one another using a variety of specialized, interchangeable adaptors. The modules may also be offset horizontally, vertically or perpendicularly to one another.