It is generally recognized that the characteristics of workload processing requests are among those parameters that critically affect the behaviour of a computer system. Therefore, the quantitative description of the processing requests, i.e. the workload characterization, is of fundamental importance in all performance evaluation problems, and is indispensable in the design of useful workload models. Now, for the first time, all problems related to workload characterization and modeling have been gathered together and analyzed in one volume. This book presents both the basic principles and the state-of-the-art in workload characterization of computer systems and computer networks, with special emphasis on experimental aspects. The methodologies and techniques currently used to characterize workloads for performance evaluation studies (tuning, design, selection, and capacity planning) are all adequately described. Invited Lectures: Workload Characterization in Distributed Environments (A.K. Agrawala and A.K. Thareja). Characterizing the Time Varying Nature of TSO Workloads (H.P. Artis). Workload Characterization Using SAS PROC FASTCLUS (H.P. Artis).