Due to the wireless techniques develop rapidly and universality of mobile devices, so people use mobile devices to access Internet, anytime-anywhere. Recently, vehicular network is broadly to apply to the Intelligent Transportation System (ITS) and it gains significant attention in the field of industry and academic. Moreover, there are many standards and protocols provided for vehicular networks. In this book, the main contributions are to provide fast handoff schemes in mobile networks and secure mutual authentication mechanisms in vehicular networks. Moreover, we integrate the authentication mechanism into the mobility management scheme without increasing the signaling overhead.