Abstract: Methods and apparatus for monitoring the performance of services provided over a network (2). The methods and apparatus make use of the computing power provided at the communications units (1) used by users to access the services. Activity instigated by users both directly and indirectly are monitored and/or reproduced at each communications unit (1). Information gathered in the monitoring processes is sent to a central unit (4) for further processing. Typically the services are accessed via the World Wide Web and part of the apparatus is controlled by a Java/Javascript applet running on a communications unit (1).