In this chapter the terminology of IT cost will be explained. Although the term ‘cost of IT’ is regularly used in several books by consultant firms, etc., most people have different definitions. In the first section we will explain different views of IT costs. After the introduction on IT costs, two IT accounting models will be introduced. These models give insight into IT costs and structure and section 4.3 will describe how they can be used. Following the introduction of the two models, the control of IT costs will be explained in section 4.4. Finally, the techniques for IT optimization will be described.