The state of the art of thin-film pyroelectric infrared (IR) detectors is reviewed covering device physics, material performance, micro-fabrication and device examples. Emphasis is given to special issues related to thin films, such as small heat capacities and the substrate influence on the pyroelectric properties. For the latter, an overview of the hitherto reported values is given. Examples of micromachined IR detectors based on pyroelectric thin films are described. The ultimate limit of micromachined thermal IR detectors is estimated for uncooled operation. It is concluded that the best pyroelectric thin films achieved to date are in principle sufficiently good to approach this limit, meaning that the present performance of pyroelectric thin-film focal plane arrays can still be improved by more than a factor of 10. A comparison of the different principles for IR detection shows that pyroelectricity is indeed one of the most competitive principles for uncooled IR detection. The major obstacle hindering quick industrialization is the fabrication complexity.