In this chapter we've delved into the communication capabilities of Windows Workflow. We've seen how correlation attributes and correlation tokens can tie together related activities, and examined role‑based authorization. Underneath the event-driven activities we've seen how workflow queues manage events and data arriving at the workflow. We can use these queues for our own communication purposes, or query the queues to see which activities are waiting for events inside a workflow. Finally, we examined the web service capabilities of Windows Workflow by building a simple web service, and a client to consume the web service.