In this paper, we develop the notion of congestion equilibrium in large scale networks, with the specific goal of understanding the modern multiparty Internet ecosystem comprising of content providers, ISPs and users. We show that the concept of “congestion-taking” is analogous to the concept of “price-taking” in classical market economics. With a wide variety of congestion metrics and under very mild assumptions on the congestion dynamics, we characterize various properties of congestion equilibria and develop algorithms to compute them for large scale networks. Our work provides a new way to model and analyze modern large scale network-economic systems that have a complex interaction of engineering and economics.