Half of the elements heavier than iron are produced by the r-process by a sequence of neutron captures, beta-decays and fission. It requires an astrophyical site that ejects material with extreme neutron rich conditions. Once the r-process ends, the radioactive decay of the freshly synthesized material powers an electromagnetic transient with an intrinsic luminosity corresponding to thousand novas. Such kilonova was observed for the first time following the gravitational signal GW170817 originating from a merger of two neutron stars. This observation answered a long lasting question in nuclear astrophysics related to the astrophysical site of the r process. In this talk, I will summarize our current understanding of the r process, the answers provided by recent observations and the remaining open questions.