The autofocus system has gained popularity in over 40 years. Embedded in a camera, it is able to bring the best focused image to the viewer within a few seconds, which frees users from focusing manually. An autofocus system usually consists of a motor, a lens and the processing and control units. Within years of development, the autofocus system has become mature in terms of both technology and market, and many fast and accurate autofocus systems have been introduced and widely installed in compact cameras and digital single lens reflex (DSLR) cameras. On the other hand, the market for thermal infrared cameras has been increasingly growing in recent years owing to their decreasing cost and wide use by both civilians and the military. The autofocus system in those cameras adopted similar but more challenging mechanisms. This article serves as a literature review of the state of the art of the autofocus system in both visible light digital cameras and thermal infrared cameras.