Large millimetric and submillimetric telescopes can play a crucial role in our understanding of the Universe, allowing the direct measurement of early galaxies or the investigation of the earliest stages of star formation. The B modes of CMB polarization are a direct probe of the Inflationary epoch and their measurement promises to provide information on the scale of energies at which the process took place. For these investigations (and many others), large detectors arrays with thousands of pixels are needed, to achieve high mapping speeds. This is especially true in the case of mm and sub/mm observations from extremely cold and dry locations like Dome-C, where ultra-low temperature detectors, reaching photon noise limited performance, are needed to fully exploit the excellent quality of the site. In this paper we present the working principle of the Microwave Kinetic Inductance Detectors and their status of development in Italy, focusing on the key aspects that make them ideal for large arrays of sensors.