This text presents information on the design, selection, function and use of biological safety cabinets (BSC's), which are the primary means of containment developed for working safely with infectious microorganisms. Brief descriptions of the facility and engineering concepts for the conduct of microbiological research are also provided. BSCs are only one part of an overall bio safety program which requires consistent use of good microbiological practices. BSCs are designed to provide personnel, environmental and product protection when appropriate practices and procedures are followed. Three kinds of biological safety cabinets, designated as Class I, II and III have been developed to meet varying research and clinical needs. High efficiency particulate air (HEPA) filters or ultra-low penetration air (ULPA) filters are used in the exhaust and/or supply systems of biological safety cabinets. Laboratory hazards and risk assessment are also discussed. An overview is provided to clarify the expectations, functions and performance of these critical primary barriers. This document has been written for the engineer, manager, or procurement officer who desires a better understanding of each type of cabinet and the rationale for selecting the appropriate BSC to meet specific operational needs.