Congestion control determines the fairness of resource sharing in networks such as the Internet. This project will study how such control can cause a build-up of unmet demand to an extent that disables services. It will build a solid theoretical understanding based on stochastic and deterministic systems theory and use that to design efficient mechanisms for improving long-term quality of service (QoS) on the Internet. This framework will then be applied to wireless networks and "demand response" in the power grid, which are mathematically more challenging. The former will give users greater freedom to access the Internet, and the latter will reduce the multi-billion dollar price of upgrading to the smart grid over the coming decade.