A mobile, modular, cleanroom facility is made from one or more pre-assembled modules, transportable in their pre-assembled form. Each pre-assembled module includes an air filtration system including a ceiling plenum for providing clean air to the interior of the module. The air filtration system provides air cleaned to at least an ISO 8 classification. When the mobile, modular cleanroom facility is made of two or more modules, each of the modules is pre-assembled, and is transportable in its pre-assembled form. Each of the modules also includes an air filtrations system having a ceiling plenum for providing clean air to the interior of the module. Most preferably, the modules are connected by a connection assembly effective for providing a seamless transition from one module to the other while maintaining the appropriate clean air classification in the transition space.