The physics of pyroelectric detectors is reviewed, including a discussion of response and electronic noise and their dependence on device design and material parameters. Other sources of noise are described, particularly as generated by environmental effects such as microphony, together with techniques for their minimisation. The range of ferroelectric materials which have been assessed for use in pyroelectric detectors is reviewed and their properties compared, particularly from the aspect of application to different types of devices. Finally, an account is given of the wide range of applications for which pyroelectric detectors have been used, including a detailed description of both the pyroelectric vidicon and pyroelectric arrays and their application to thermal imagers.