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 realising what he named as time crystals. Their existence has been confirmed very recently in a number of experiments. I will briefly review the field focusing in particular on the so called Floquet time-crystals (arising in many-body systems that are periodically driven) and on time-crystalline behaviour in quantum open systems. For this last case, I will make connections to quantum synchronisation.