The functions of actin and its motor proteins myosins in the cytoplasm have been the subject of research for more than 100 years, but the existence and function of these proteins in the nucleus has been a matter of debate until recently. Recent data has clarified the role of actin and myosin molecules in controlling the dynamics of processes in the cell nucleus, chromatin organization and genome integrity. New microscopy techniques and the use of modified actin-binding probes have made it possible for the first time to directly visualize the polymerization of actin filaments in the nucleus of living cells. Here we discuss the processes that control the dynamic balance of actin and myosins between the nucleus and the cytoplasm, as well as the role of these proteins in the regulation of transcription, DNA repair, chromatin reorganization, tumor transformation and cell differentiation.