  Cluster structure in stable and unstable nuclei has been studied. We report
recent developments of theoretical studies on cluster aspect, which is
essential for structure study of light unstable nuclei. We discuss negative
parity bands in even-even Be and Ne isotopes and show the importance of cluster
aspect. Three-body cluster structure and cluster crystallization are also
introduced. It was found that the coexistence of cluster and mean-field aspect
brings a variety of structures to unstable nuclei.
