Biosafety as a professional discipline as a result of increased numbers of regulations and guidelines directed toward reducing the potential for occupational illness and adverse environmental impacts from microorganisms and biological materials. Biosafety cabinets (BSCs) are primary barrier protection for individuals working with biologic materials and are designed to provide personnel, environmental and product protection when appropriate practices and procedures are followed. This review presents information on the selection, function and use of BSCs. Three kinds of BSCs, designated as Class I, II and III have been developed to meet varying research and clinical needs. Aim of this overview is to clarify the expectations, functions and performance of these critical primary barriers. This document has been written for the laboratorian, engineer or manager who desires a better understanding of each type of cabinet and the rationale for selecting the most appropriate BSC to meet specific operational needs.