Metallic magnetic calorimeters (MMCs) are cryogenic detectors that offer an excellent energy resolution, a signal rise time of below 100 ns, a high dynamic range and almost optimal linearity. MMCs are of high interest for many experiments, such as dark matter detection or direct neutrino mass investigations. Since larger detector arrays are read out at GHz-Frequencies, and each single pixel offers a fast rise time, a complex analog and digital readout system is required. This contribution will give an introduction to MMC technology in combination with the implemented readout electronics and the current status of the present readout architecture.