Future computer environments will include mobile computers which will either be disconnected, weakly inter-connected by low speed wireless networks such as GSM, or fully inter-connected by high speed networks ranging from Ethernet to ATM. Such environments place unique demands on systems, requiring software to dynamically adapt to rapid and significant fluctuations in communications quality-of-service (QoS). This paper reviews existing adaptation techniques and describes an experiment in developing an adaptive mobile application and associated distributed systems platform. The experiences gained during this experiment are presented and analysed to provide a basis for the engineering of future adaptive systems.