The use of pyroelectric thin-film electrets for calorimetry of transient heating processes is explored. A pyroelectric calorimeter which combines a time resolution of nanoseconds with a sensitivity of nanocalories is described. The versatility and the unique properties of this new type of device are demonstrated with several applications in the thermal analysis of thin films and spectroscopy of adsorbates. Data are presented on the thermal diffusivity of thin films and on phase transitions during optical recording. In addition, results on spectroscopy of thin films and adsorbates are reported. © 1986 IEEE.