This thesis presents a handoff technique between the IEEE 802.11 WLAN, which covers a small area, and the GPRS cellular network that overlays the WLAN and covers a larger area. The technique reduces the handoff delay, recovers the lost packets during the handoff transition period with improved overhead, increases the throughput, and also prevents unnecessary handoffs from due to ping-pong effect. It includes an algorithm to be implemented in the handoff decision making process as well as modification of the Mobile IP for handoff signaling management to achieve improved performance in latency, overhead, and throughput. (Abstract shortened by UMI.)