There are currently six primary government systems of occupational classification used to classify civilian work in the United States. This chapter discusses the systems most pertinent to vocational guidance and Transferable skills analysis (TSA). To improve cross-references from one system to another, the Federal Office of Management and Budget requires that each system directly relate to the standard occupational classification in some way TSA is a time-honored and time-tested method for reasonably identifying similar or new jobs for people following illness or disability, for those seeking alternate work opportunities for “change”, advancement, or transition to a new employment setting. The most critical ingredient in the determination process is the activity and preparation of the practitioner. In cases where the online O*NET or a commercial computer program is used, information that is input to the program is determined by the practitioner.