In this chapter we provided an overview of the important aspects of a system integrating Mobile IP and a AAA infrastructure to provide secure roaming. Unfortunately this interaction is rather complicated and the standards are not quite stable yet, but we tried our best to provide the right amount of detail without diving too deep into every technical detail. In fact, we must confess that the level of complexity involved in Mobile IP-AAA interaction was the main reason we decided to write this book: to help engineers not familiar with AAA protocols to understand the procedure without having to first plow through lengthy and frequently changing IETF documentations. The fact that Diameter itself is almost non-existent in the real world and there are no IETF RADIUS-Mobile IP documentations does not make the implementation of Mobile IP-AAA signaling any easier. There are almost no vendors that at this point claim support for Mobile IP-AAA signaling, since there are very few commercial networks that deploy this interaction. From what the authors found out, the very few vendors that advertise mobility functionality for their AAA server are those that support parts of the CDMA2000 way of implementing Mobile IP-RADIUS interaction. However, the authors are hoping to initiate the standardization process for RADIUS-Mobile IP interaction in IETF very soon [RADIUS MIPDR].