Book excerpt: A timely presentation of new results, challenges, and opportunities in the quickly developing field of nuclear cluster physics, presented by an international group of eminent theoretical and experimental scientists active in the field. Their work reveals how correlations of nucleons can appear spontaneously, propagate, and survive in nuclear matter at both low and high densities. Characteristic nuclear substructures, beyond those predicted by mean-field or collective scenarios, appear on microscopic and cosmic length scales. They can influence the dynamics of fusion of light nuclei and the decay of heavy, fissioning nuclei or of systems produced transiently in heavy-ion reactions. A must-read for young scientists entering the field and a valuable resource for more seasoned nuclear researchers!