Abstract: This paper discusses the history, current state-of-the-art, and ongoing challenges for compact (less than a few cm^3) magnetic power generation systems in the mW to tens of W power range. These systems are of great interest for powering sensor networks, robotics, wireless communication systems, and other portable electronics. First, the theoretical and practical implications of miniaturizing magnetic power generators are briefly reviewed. Then, the design and performance of previously demonstrated devices are summarized and compared. Finally, ongoing challenges for implementation are briefly discussed, including integrated high-performance hard magnetic materials; microscale core laminations; low-friction bearings; high-speed rotor dynamics; and compact, high-efficiency power converters.