This paper concentrates on recent developments in the field of implantable sensor and actuator systems. As examples for sensing systems the measurement of the intraocular pressure by an implanted system will be presented as well as a monitoring system for in situ strain monitoring on femoral nailplates. As actuating systems a multichannel neuromuscular microstimulator with bi-directional telemetry as well as a very complex system for stimulating the nerve cells of the retina of patients suffering from retinitis pigmentosa will be shown. The systems mentioned before are all powered by HF-frequency. The last example is a battery powered multisensor implant for monitoring transplanted hearts.