Publisher Summary Integrated Services work is the first major attempt to enhance the Internet with QoS capabilities. The networking research community has made substantial progress in developing algorithms and mechanisms to support advanced resource allocation in the network. This chapter presents the architecture, mechanisms, and protocols of Integrated Services. It analyzes the requirements of real-time applications that have influenced several aspects of the development of Integrated Services. An overview of the Integrated Services architecture and the basic approaches behind it are presented, followed by a discussion of the new service models that Integrated Services support. The guaranteed service model provides deterministic worst-case delay bound through strict admission control and fair queuing scheduling. This service was designed for applications that require absolute guarantees on delay, whereas controlled load service is designed for adaptive applications that can tolerate some degree of delay variation. This chapter sheds light on the mechanisms and algorithms for implementing Integrated Services in routers and switches, and describes the problem of identifying reserved flows. Packet scheduling algorithms support delay and bandwidth guarantees. The use of Integrated Services in enterprise networks and the mapping of Integrated Services to asynchronous transfer mode (ATM) networks are also explored in the chapter.