The term 'representativeness' has multiple meanings in the context of judgment. Three senses of the word will be distinguished: (i) a non-regressive matching from a heuristic attribute to a target attribute; (ii) the use of a representative instance (prototype, stereotype) to stand for a set or category; (iii) the use of similarity (representativeness) between an individual and the prototype of a category to judge the probability that the individual belongs to the category. Judgment by representativeness is a special case of a broader process of judgment by prototype. The boundary conditions for the neglect of base-rate information correspond closely to the boundary conditions for a broader phenomenon of extension neglect. The similarity extends to what happens when base-rate and other extensional variables are not neglected. Old and new data that support these ideas will be presented.