This book presents an extension of stochastic process algebra PEPA called suitable for determining the Markov process, which can then be applied to modeling performance. This method, which the author illustrates with case studies taken from the field of communication systems, can easily be used to build various models which can be analyzed using standard numerical techniques. One major advantage of PEPA on the standard method for determining the performance of the stochastic model is the apparatus attached to reasoning about the structure and behavior of the model.