The criteria for the selection of ferroelectric materials for use in thermal detector arrays for applications such as thermal imaging and people counting have been reviewed. It has been shown that excellent properties can be obtained through the use of perovskite creamics and thin films, especially modified lead zirconate and lead titanate based compositions. The importance of measuring the dielectric properties at an appropriate frequency has been emphasized. It has been indicated that how material characteristics other than the pyroelectric and dielectric properties are important in determining the performance of a device. PMZT thin films can be made at relatively low temperatures with pyroelectric properties that approach those of bulk ceramics.