Landau's idea of classifying phases of matter in terms of symmetry breaking is a cornerstone of modern physics. In his pioneering work Wilczek argued that an autonomous system can break time translation symmetry, thus realizing what he called “time crystals”. Their existence has been confirmed very recently in a number of experiments. Fazio will review the field focusing in particular on the so-called Floquet time-crystals arising in many-body systems that are periodically driven.