This paper makes the case that operating system designs for sensor networks should focus on the coordination of resource management decisions across the network, rather than merely on individual nodes. We motivate this view by describing the challenges inherent to achieving a globally efficient use of sensor network resources, especially when the network is subject to unexpected variations in both load and resource availability. We present Peloton, a new distributed OS for sensor networks that provides mechanisms for representing distributed resource allocations, efficient state sharing across nodes, and decentralized management of network resources. We outline the Peloton OS architecture and present three sample use cases to illustrate its design.