AlxGa1-xN alloys are very attractive materials for application to ultraviolet photodetection. AlGaN photoconductors, Schottky photodiodes, metal-semiconductor-metal photodiodes, p-n junction photodetectors and photo transistors have been recently developed. In this work we analyse the performance of AlGaN-based photodetectors, discussing present achievements, and comparing the characteristics of the various photodetector structures developed to date.