The chapter provides the insight into software maintenance process, its features, actors, activities and results, with the emphasis on the importance and complexity of systems maintenance. The issues related to maintenance modeling, maintenance process evaluation and improvement are addressed. The chapter proposes a method for system maintenance modeling and analysis. Software maintenance process is modeled in terms of queuing network with applied simulation. Method implementation is described by a case study of telecommunication maintenance with the field process data. The case study and the related maintenance activities with data are described in detail. The results of the method application show how the process bottlenecks are formally identified and how new proposals for the improved process design should be analyzed. The chapter emphasizes the importance of a well-defined and balanced process indispensable for efficient maintenance of the large telecommunication software.