Today’s wireless networks are highly heterogeneous, with mobile devices consisting of multiple wireless network interfaces (WNICs). Since battery lifetime is limited, power management of the interfaces has become essential. We develop an integrated approach for the management of power and performance of mobile devices in heterogeneous wireless environments. Our policy decides which WNIC to employ for a given application and optimizes its usage based on the current power and performance needs of the system. The policy dynamically switches between WNICs during program execution if data communication requirements and/or network conditions change. We have experimentally characterized Bluetooth and 802.11b wireless interfaces. Our policy has been implemented on HP’s IPAQ portable device communicating with HP’s HotSpot server [14]. The applications we tested range from MPEG video to email. The results show that our policy offers a large improvement in power savings as compared to singly using 802.11b or Bluetooth while enhancing performance.