Monolithic Active Pixel Sensors (MAPS) take advantage of recent developments in deep sub-micron VLSI technology. CMOS sensors now enjoy widespread commercial applications as inexpensive visible light-imaging devices. These are also being utilised and developed for an increasing number of scientific fields due to advantages which include: low power consumption, radiation hardness, small pixel size and on-chip or even in-pixel processing capabilities.We have designed, characterised and evaluated a number of prototype CMOS MAPS devices as position-sensitive detectors for ionising radiation. This development was primarily driven by the requirements of the Linear Collider vertex detector but a broader spectrum of applications, including several outside particle physics, has been explored and some of these are also briefly presented here.