In this paper, we discuss flow control in a resourcesharing computer network. The resources consist of a set of inhomogeneous computers called hosts that are geographically distributed and are interconnected by a store-and-forward communications subnet. In the communication process, messages pass between hosts via the subnet. A protocol is used to control the flow of messages in such a way as to efficiently utilize the subnet and the host resources. In this paper, we examine in some detail the nature of the flow control required in the subnet and its relation to the host flow control and subnet performance.