Queuing networks are popular us models of performance of computer systems and communication networks. The Research Queueing Package, Version 2 (RESQ2), is a system ,for constructing and solving extended queuing network models. We refer to the class of RESQ2 networks as “extended” because of characteristics absent from most queuing models, RESQ2 incorporates a high-level language to concisely describe the structure of the model and to specify constraints on the solution. A main ,feature of the language is the capability to describe models in a hierarchical ,fashion, allowing an analyst to define parumetric submodels which are analogous to mucros or procedures in programming languages. RESQ2 thus encourages use o f structured models to effectively evaluate complex systems.