The talk will provide an overview of psychological theories of similarity and key behavioural data. It will introduce spatial models (e.g., Shepard, 19887), featural models, in particular Tversky's (1977) Contrast Model, structural alignment approaches to similarity (e.g., Gentner & Markman, 1997), as well as the more recent transformational approach (Hahn et al. 2003). The talk will introduce these models, clarify their relationship, and outline the behavioural phenomena they do (and do not) capture.