: The Third Generation (3G) cellular networks provide ubiquitous connectivity but low data rates, whereas Wireless Local Area Networks (WLANs) can offer much higher data rates but only cover smaller geographic areas. Their complementary characteristics make the integration of the two networks a promising trend for next-generation wireless networks. With combined strengths, the integrated networks will provide both wide-area coverage and high-rate data services in hotspots. There are many aspects involved in their interworking, such as mobility, security and Quality of Service (QoS) provisioning. In this paper, we present a survey of most recent interworking mechanisms proposed in the literature, and outline some important open issues to achieve seamless integration.