Cluster structure of nuclei

In studies of nuclear reactions, especially when the motivation is to investigate the reaction mechanism, it is sometimes convenient to assume a cluster structure for the target and projectile. It is realised that the assumption of cluster structure is often not more significant than a convenient method to simplify the complexity of a proper shell model theoretical formulation. Also, especially for heavier nuclei, it is not always clear whether cluster preformation probabilities which are implied by the extracted quantities are realistic. My review of the issues that are involved will be restricted mostly to how these are interwoven with the interpretation of experimental work that I have personally been involved with. Preliminary results of recent sophisticated breakup measurements will also be presented.