This thesis is a review of six publications which focus on the development of ther-mal detectors and on-chip coolers. The thermal detectors developed are antenna coupled microbolometers and transition-edge microcalorimeters. The bolometers are intended for the detection of submillimetre waves, a region in the electromag-netic spectrum located between the infrared and microwave frequencies, in which detection methods are least developed. A room temperature bolometer is pre-sented, which is suitable for applications where large levels of signal power are present, such as solar astronomy or imaging of concealed weapons under cloth-ing when combined with an illumination source, while the sensitivity of a novel superconducting bolometer, operated at 4.2 K, is more than sufficient for passive imaging of terrestrial sources. The figure of merit for this detector is shown to be about an order of magnitude better than that of existing 4.2 K bolometers. Results obtained with X-ray transition-edge sensor (TES) microcalorimeters, the most sensitive type of X-ray detector in terms of energy resolution to date, are presented. These devices are operated at temperatures below 100 mK, and can achieve energy resolutions of a few electron volts. The TES microcalorimeters wil
