This chapter reviewed the capabilities of the Windows Workflow runtime. We examined how to monitor the workflow runtime by subscribing to runtime events and configuring tracing information. We also examined how to customize the runtime by adding services. These services include scheduling services (to manage threads), persistence services (to manage state), and tracking services (to record tracking information). If the built-in services do not fulfil our requirements, we can replace any of them with custom versions we write ourselves. This architecture gives the Windows Workflow runtime its flexibility and extensibility.