The principles of operation of a bolometer are summarized and responsivity, noise equivalent power and detectivity are derived. The effects of geometrical and material factors on the performance of the bolometer are discussed. The latest developments of high temperature superconducting bolometers are summarized. Experimental results using YBa2Cu3O7-x, superconducting thin films as a bolometer are presented. A brief summary of possible future improvements in the performance of the bolometer is finally given.