The Electron Capture 163-Ho experiment, ECHo, aims to investigate the electron neutrino mass in the sub-eV range by means of the analysis of the calorimetrically measured energy spectrum following the electron capture process of 163-Ho. In the ECHo experiment, arrays of low temperature metallic magnetic calorimeters with high energy resolution and fast response time, having the 163-Ho source embedded in the absorber, will be used to calorimetrically measure the EC spectrum. A precise description of the expected spectrum will be achieved by theoretical calculations based on Density Functional Theory (DFT) and Quasiparticle Random Phase Approximation(QRPA) supported also by experimental investigations. Moreover, independent measurements of the Q-value will be performed using high precision Penning trap. For the measurements of Q as well as for the calorimetric measurement of the 163-Ho spectrum, high purity 163-Ho sources will be produced. Detailed studies of the background and of methods to reduce it will be performed in order to increase the sensitivity of the calorimetric measurement.