Agile development processes are popular when attempting to respond to changing requirements in a controlled manner; however, selecting an ill-suited process may increase project costs and risk. Before adopting a seemingly promising agile approach, we desire to evaluate the approach's applicability in the context of the specific product, organization, and staff. Simulation provides a means to do this. However, in order to simulate agile processes we require both the ability to model individual behavior as well as the decoupling of the process and product. To our knowledge, no existing simulator nor underlying simulation model provide a means to do this. To address this gap, we introduce a process simulation reference model that provides the constructs and relationships for capturing the interactions among the individuals, product, process, and project in a holistic fashion - a necessary first step towards an agile-process evaluation environment.