$^{163}$Ho based experiments

The analysis of the endpoint region of the calorimetrically measured $^{163}$Ho electron capture spectrum is a very promising way to determine the mass of the electron neutrino. The achievable sensitivity of $^{163}$Ho-based experiments and the experimental challenges will be presented. Three large collaborations aim to develop large scale experiments able to reach sub-eV sensitivity. Presently pilot experiments are performed to demonstrate the possibility to calorimetrically measure high precision and high statistics $^{163}$Ho spectra. The different approaches as well as the state of the art of the experimental efforts for the three collaborations will be discussed.