ESnet – the Energy Sciences Network – has the mission of enabling the aspects of the US Department of Energy's Office of Science programs and facilities that depend on large collaborations and large-scale data sharing to accomplish their science. The network requirements of this community have been explored in some detail by ESnet and a long-term plan has been developed in order to ensure adequate networking to support the science. In this paper we describe the planning process (which has been in place for several years and was the basis of a new network that is just now being completed and a new set of network services) and examine the effectiveness and adequacy of the planning process in the light of evolving science requirements.