The aim of this thesis is to define a solution offering end-users seamless mobility in a multi-radio access technology environment. Today an increasing portion of cell phones and PDAs have more than one radio access technology and wireless access networks of various types are commonly available with overlapping coverage. This creates a heterogeneous network environment in which mobile devices can use several networks in parallel. In such environment the device needs to select the best network for each application to use available networks wisely. Selecting the best network for individual applications constitutes a major core problem.The thesis proposes a host-based solution for access network selection in heterogeneous wireless networking environments. Host-based solutions use only information available in mobile devices and are independent of information available in the networks to which these devices are attached. The host-based decision mechanism proposed in this thesis takes a number of constraints into account including network characteristics and mobility patterns in terms of movement speed of the user. The thesis also proposes a solution for network-based mobility management contrasting the other proposals using a host-based approach. Finally, this thesis proposes an architecture supporting mobility for roaming users in heterogeneous environments avoiding the need for scanning the medium when performing vertical handovers.Results include reduced handover latencies achieved by allowing hosts to use multihoming, bandwidth savings on the wireless interface by removing the tunneling overhead, and handover guidance through the usage of directory-based solutions instead of scanning the medium. User-perceived quality of voice calls measured on the MOS (Mean Opinion Score) scale shows no or very little impact from the mobility support procedures proposed in this thesis. Results also include simulation models, real-world prototypes, and testbeds that all could be used in future work. The proposed solutions in this thesis are mainly evaluated using simulations and experiments with prototypes in live testbeds. Analytical methods are used to complement some results from simulations and experiments / Godkänd; 2010; 20100811 (karand); DISPUTATION Ämnesområde: Mobila system/Mobile Systems Opponent: Universitetslektor, docent Marcus Fiedler, Blekinge tekniska högskola Ordförande: Universitetslektor, docent Christer Åhlund, Luleå tekniska universitet Tid: Fredag den 12 november 2010, kl 11.00 Plats: A1514 Demostudion, Luleå tekniska universitet