An ac motor drive consists of a dc-ac inverter, an ac motor and some mechanical load. The inverter supplies electrical power in an appropriate form to the motor, which in turn provides the conversion to mechanical power needed to drive the load. All three components of the system are characterized by models which are non-linens and contain unknown parameters. Improved motion control performance may thus be attempted by using non-linear adaptive control methods. In this paper, a linearizing adaptive motion controller is derived for a representative nc motor drive, under the assumption that the parameters describing the inverter, the motor, and its lend, are all unknown. The controller guarantees global stability and asymptotic tracking.