Just as the management of individual patients requires specific and timely information upon which clinical decisions can be based, so managers and clinicians, responsible for service planning, require appropriate information on the activity levels and functions of their services. This is true at all levels, from individual clinicians and teams who wish to audit their activities, through clinical directors and managers of departments and units, to those who plan for Districts and Regions. Casemix is an attempt to facilitate this process by developing a meaningful language, to describe and measure clinical activity.