Recent developments in nuclear cluster theory

The major novelties that have emerged in nuclear cluster theory since the last, 9th, cluster conference is reviewed. Among the marked developments made in many traditional and novel subjects of nuclear cluster physics, four subjects are chosen in this introductory talk. They are 1. neutron-rich nuclei, 2. cluster gas, 3. coexistence of cluster and mean-field dynamics, and 4. ab initio approaches. A representative example of the present status of the field is that it is studied in the framework of ab initio nuclear theory as well. We discuss a recent ab initio calculation of the Hoyle state of 12C, which supports its cluster-gas-like structure.