This invention relates to the area of Mobility and Handover between heterogeneous wireless networks. The scope of the invention also covers the case when the UE is capable of accessing both the WLAN and EUTRAN access systems simultaneously and also the case where the UE is not capable of accessing both the WLAN and EUTRAN access systems simultaneously. This invention provides a system and method to perform Mobility between the access systems with optimized authentication procedure using security context transfer between the access systems and also minimize the data loss by buffering the data during the handover. More specifically, this invention provides a system and method to support handover between the I-WLAN and the EUTRAN access systems.