Inventive embodiments are directed to components, subassemblies, systems, and/or methods for auxiliary power units (APU). In one embodiment, the APU includes a source of rotational power such as a combustion engine operably coupled to a continuously variable transmission (CVT). The CVT can be coupled to a load. In some embodiments, the load is provided by a generator. In one embodiment, the APU has a control system configured to control the operation of the engine and the operation of the CVT. The control system can facilitate substantially constant speed operation of the generator in the presence of variable operation of the engine. In another embodiment, the APU includes a continuously variable accessory drive (CVAD) operably coupled to an engine. The CVAD can include a continuously variable transmission operably coupled to a generator. In one embodiment, a skew-based control system is adapted to facilitate a change in the ratio of a CVAD.