Electromagnetic Interference (EMI) is a description of the phenomenon which results from allowing conducted and radiated electrical signals to reach destinations where their presence is undesirable. Uncontrolled EMI may cause computer malfunction or error, detonation of electrically explosive devices, or be the cause for loss of classified information to an enemy. The objective of this handbook is to provide a basic understanding of the problems associated with the acquisition of a facility containing one or more EMI shielded enclosures. It is intended that only the characteristics of the facility that are unusual in comparison to a non-shielded facility will be addressed. This handbook is a brief introduction to EMI shielding theory, and presents basic criteria of importance during the planning, design, and construction of a typical facility containing an EMI shielded enclosure.