This document provides an overview of mobile roaming concepts and processes. It discusses what roaming is, roaming databases, GSM vs CDMA networks, SIM cards and their components like IMSI and HNI. It also describes establishing roaming relationships for GSM networks, including finding partners and using Permanent Reference Documents like AA12 and AA13 that cover agreement management, supported services, billing, customer care, technical aspects, data privacy, and fraud prevention procedures. The document also includes sections on the RAEX agreement and the IR21 database report that contains network, routing, and technical configuration information.