Cryogenic particle detectors such as metallic magnetic calorimeters (MMCs) have rapidly advanced their performance in recent years and are now applied in a wide range of experiments from high resolution x‐ray detection to neutrino mass measurements. MMCs are composed by an energy absorber, optimized for the particles to be detected, in good thermal contact with a metallic paramagnetic sensor positioned in a weak magnetic field. A change in the sensor magnetization follows the change of the detector temperature. High energy resolution can be obtained by using a low‐noise, high‐bandwidth DC‐SQUID to measure the corresponding change of flux. Fully microfabricated MMC detectors operated below 100 mK are now available for x‐ray detection with an energy resolution of 2.7 eV at 6 keV. We will discuss the basic principle of such detectors and their optimization for different applications. In particular, the status of development for MMCs arrays with multiplexed readout and MMC based position sensitive detectors will be presented. In addition, we will show the results of current applications of MMCs.