We consider wearable computing applications which rely on audio as a primary medium of the interface. This paper surveys a range of interaction techniques which may be applied to the design of wearable audio computers (WACs). A summary of several speech and audio processing technologies which can be used in the interface of WACs are reviewed. We present several usage scenarios and focus on two specific systems which we are currently implementing. Nomadic Radio is a 3-D audio application which provides the user with a personalized and dynamic audio-only information environment. We are also developing an adaptive speech recognition system; an application based on this system enables hearing impaired users to visualize speech. Future research areas include adaptive interfaces, automatic situational awareness and focus of attention in wearable audio computing.