IP network mobility is emerging as a major paradigm for providing continuous Internet access while a set of users are on the move in a transportation system. The intense interest on its support has led to the establishment of the NEMO IETF working group and a test-deployment by a major airline equipment vendor - Boeing - on major airline routes. However, the previously proposed solutions are either inefficient or may cause instability to the global Internet. In this paper, we propose WINMO, a simple, systematic, novel solution for wide-area IP network mobility using techniques including route aggregation, scoped update propagation, and packet mobility states. Our solution provides efficient routing when users travel both across autonomous systems (ASes) and within a single AS, generates minimal global routing overhead to prevent global instability, ensures good location privacy, and helps to defend against denial-of-service attacks. Furthermore, our basic scheme (without packet mobility state) is transparent to both clients and servers. Our extensive evaluations demonstrate the effectiveness of our mobility solution.