The international project “Microcalorimeter Arrays for a Rhenium Experiment” (MARE) aims at the direct and calorimetric measurement of the electron anti-neutrino mass with sub-electronvolt sensitivity. The experimental strategy consists in studying the beta spectrum of 187 Re near the end-point looking for the spectral distortion expected for a finite anti-neutrino mass. The MARE project has a staged approach: in the final experimental phase (MARE-2), several large arrays with as many as 10000 detectors each will be deployed to collect the statistics required to probe the anti-neutrino mass with a sensitivity of at least 0.2eV, comparable to the one expected for the Katrin experiment (KATRIN LoI, 2001, [1]). In the short term, smaller scale experiments are planned to reach sensitivities of the order of 1eV (MARE-1). This contribution reports on the Milano group activity for the MARE project.