The principle concepts of performance engineering are presented in this chapter. A motivating example is described involving the planning, development, and implementation of a call center application. Five examples of how performance considerations should be included in the analysis, design, operation, and evolution of a system are presented. The main issue in performance engineering is how to guarantee that a system will meet its performance goals. The steps required to carry out a performance engineering effort are described. A central issue in the methodology are the models needed to represent workload and the performance of a system. The basic steps of a practical performance engineering methodology include the following.