The clustered nucleus - cluster structures in stable and unstable nuclei

The subject of clustering has a lineage which runs throughout the history of nuclear physics. Its attraction is the simplification of the often uncorrelated behaviour of independent particles to organized and coherent quasi-crystalline structures. In this review the ideas behind the development of clustering in light nuclei are investigated, mostly from the stand-point of the harmonic oscillator framework. This allows a unifying description of alpha-conjugate and neutron-rich nuclei, alike. More sophisticated models of clusters are explored, such as antisymmetrized molecular dynamics. A number of contemporary topics in clustering are touched upon; the 3 alpha-cluster state in C-12, nuclear molecules and clustering at the drip-line. Finally, an understanding of the C-12 + C-12 resonances in Mg-24, within the framework of the theoretical ideas developed in the review, is presented.