This tutorial presents and extends ideas presented in an article with the same title published recently in the Communications of AIS. (Alter, 1999). The basic idea is that the concept of “work system” provides an effective framework for studying almost any kind of information system. The meaning and significance of an information system is not in the information system itself, but rather, in the work system(s) it supports. The tutorial explains the elements of a work system and shows how the work system concept can be used as a common denominator for systems in operation and for projects. It shows how this concept can be used to understand topics including alternative roles of information systems, plumbing vs. content in information systems, success factors and other generalizations about systems, and various aspects of IS research.