Why does our material world have a hierarchical structure; quarks, hadrons, nuclei, atoms, molecules? This is a fundamental question yet to be understood in fundamental science. This project, “Clustering as a window on the hierarchical structure” aims to understand the formation mechanism of the hierarchical structure of such quantum particles. For this purpose, we integrate our research activities on hadron, nuclear, atomic, physics, and molecular science, where Japan has played leading roles, and establish a research consortium to fill the large gaps among the conventional research fields. A variety of novel clustering phenomena will be primary targets of the research, which will clarify not only universal phenomena but also characteristic features of each hierarchy. We thus open a new research field to investigate the origin of hierarchies of matter.