WCF enables disconnected work between clients and services. The client posts messages to a queue, and the service processes them. Such interaction enables different possibilities, and in turn a different programming model, from those presented so far. This chapter starts by showing you how to set up and configure simple queued services, and then focuses on aspects such as transactions, instance management, and failures, and their impact on both the business model of the service and its implementation. The chapter ends with my framework for a response service and the HTTP bridge for queued calls over the Internet.