The nucleus is a quantum many-body complex system governed by the nuclear force, and it is prone to global changes such as deformation, rotation, vibration, fission, and clustering. In the past >30 a, we have witnessed the rapid expansion of the experimentally attainable nuclear chart and new discoveries and breakthroughs in studies on unstable nuclei. Examples include the halo nuclei and the associated exotic structural phenomena, the shell evolution observed using in-beam γ spectroscopy through the application of the achromatic magnetic spectrometer, the measurement of the basic properties of unstable nuclei, and the discovery of new magic numbers and rich phenomena in multi-nucleon correlations along with the formation of clusters and molecules. In the coming years, the expanded area of the nuclear chart—particularly the medium-heavy-mass neutron-rich region—will be the host of extreme exotic structures, the astrophysical r-process, and the reaction pathways to reach the superheavy island. Therefore, many new-generation radioactive ion-beam facilities are under development worldwide, and essential breakthroughs are foreseen.