A system for identifying a user of a controller includes a controller having one or more sensors configured to detect interaction with the controller by the user and a transmitter configured to transmit telemetry data based on outputs of one or more of the sensors, a user profile unit configured to obtain user profile data for one or more user profiles, where each user profile corresponds to a respective user and the user profile data for a user profile comprises data indicative of one or more characteristic interactions by the user with the controller, and a user profile selection unit configured to select a user profile from the one or more user profiles in dependence upon a degree of match between one or more properties of the transmitted telemetry data and the data of each respective user profile, and configured to modify an output of the system responsive to the selection.