Pocket switched networks (PSNs) provide a new networking paradigm that takes advantage of human mobility to distribute data. Due to the frequent and long-duration disruptions of network links, routing in PSNs is nontrivial. In this article, we first outline the challenges of PSN routing. After that, we summarize the behavioral traits of human beings employed by existing PSN routing schemes and give a brief survey on the state-of-the- art PSN routing techniques. Finally, we analyze the characteristics of existing PSN routing protocols and present some open problems that may foster future research on PSN routing.