The Internet Protocol (IP) address has dual significance: it is used to both uniquely identify a node in the network and to state the node's point of attachment to the network. If a node changes network it normally has to change its IP address. Protocols such as the Transmission Control Protocol (TCP) use the IP addresses of the peers to identify connections. A TCP connection therefore depends on the addresses to remain the same during the lifetime of the connection. If a node changes network and thereby change its identity, the result is disruptions in active connections. The Mobile Internet Protocol (Mobile IP or MIP) is an enhancement to IP that solves the mobility problem and allows a mobile node to roam across subnetworks while maintaining transport and higher-layer connections. This master thesis analyses and compares the two versions of Mobile IP --- Mobile IPv4 and Mobile IPv6. We build a Mobile IPv4 prototype and evaluate handoff times. This thesis also includes an analysis of test suites and products using Mobile IP. It investigates how products developed by Axis Communications AB can benefit from the use of Mobile IP. Finally, we focus on alternative or complementary solutions to IP mobility.