This paper covers circuits and systems techniques for the construction of high reliability biosensing and stimulation medical devices. Such microsystems are dedicated for interconnections through either the central or the peripheral nervous systems. Low-power high-reliability wireless links are used to power up the implanted devices while data are exchanged bidirectionaly between these implants and external controllers. A global view of main devices is given, case studies related to applications such as bladder control, intracortical monitoring and microstimulation are discussed, altogether with modeling, characterization, as well as microsystems assembly and packaging. Also, dedicated electrode arrays and their interfaces to tissues interfaces are summarized.