The many opportunities offered by wearable computing have triggered the imaginations of designers and researchers in a wide variety of fields. The inevitability of computers and interfaces which are small enough to be worn on the human body has inspired the creation of devices and applications which can assist with specialised professional and personal activities, as well as aiding and augmenting everyday life in the modern world. In reality limitations imposed by factors such as battery life, processor power, display brightness, network coverage and form factor have conspired to delay the widespread introduction of wearable computers. Nevertheless over the past ten years there have been many successful implementations and, as the relentless miniaturisation of computing devices continues, an increasing number of viable applications are emerging. In this paper wearable computing applications are reviewed from the early aircraft maintenance and military designs; through current production models including designs for personal entertainment, communication and health monitoring; to prototype implementations for real world gaming and smart fashion textiles. The challenges presented by these applications are identified and discussed.