In an electrosurgical system having a generator for generating radio frequency (RF) power and an electrosurgical instrument, the instrument includes a passive electrical identification component having a parameter of finite non-zero value identifying the instrument. The generator has a sensing circuit with a second electrical component, a signal source providing a voltage step-change, and a signal detector for detecting a transient response of the combination of the identification component and the second electrical component, the detector output signal being representative of the parameter value thereby allowing automatic identification of the instrument when it is connected to the generator. Also disclosed is an electrode assembly in which the identification component is associated with a digital device including a memory, the instrument having a pair of contacts interconnected by the identification component and serving to supply power from the generator to the digital device and/or convey data from a data output of the digital device.