Using network coding, wireless mesh networks can significantly improve their performance. However, since many wireless mesh networks have user contributed devices as their nodes, to guarantee the cooperation of such selfish nodes is a highly challenging problem. In this paper, we study how to stimulate selfish nodes to cooperate in wireless mesh networks using network coding. We propose a simple, practical reputation system that rewards cooperative behavior in routing and packet forwarding and penalizes non-cooperative behavior. Simulation results verify that our reputation system is very efficient and that it effectively stimulates cooperation.