Present status is discussed, from the theoretical viewpoint, for some selected topics of nuclear cluster physics. What is stressed here is that many of basic concepts of nuclear cluster physics since the days of K. Wildermuth are now examined and revived in new lights. An important example is the duality character of the ground-state wave function which was well known already in 1950's and has been recently revived in order to explain observed large magnitudes of E0 transitions between cluster

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... tates and the ground state in many nuclei. The other topics we discuss are (1) spatial localization of clusters v.s. THSR wave function, (2) coexistence of cluster states with mean-field-type states, and (3) spatial localization of clusters and ab initio calculations of cluster states.