An exploration of the present and future trends of WLANs and WPANs. It examines the path that these infrastructures are following from a perspective of synergies with 3G systems, and how they will pave the way for future 4G systems. The authors present an overview of 3G networks and standards, and discuss intraworking and handover mechanisms between WLANs and WPANs when they support the TCP/IP stack. Several critical issues are explored in depth, including IP routing and mobility, the ad hoc concept, IEEE 802.11 and the HIPERLAN/2 standards, PHY and MAC layers for the main WLAN specifications, the TCP-UDP/IP protocol stack, and 802.11b over TCP/IP.