Difficulties in defining think tanks complicate efforts to count them and construct meaningful samples, while attempts to define them more precisely often apply arbitrary distinctions. These difficulties are also tied to fundamental ambiguities concerning the nature of their political, scientific, and technocratic functions. This article compares four Canadian organizations (the Mowat Centre, the Parkland Institute, the Manning Centre, and the Broadbent Institute) to discover the dimensions that make up the think tank as a social type. The approach was to examine cases on the fringes of the figure of the think tank in order to assess the hypothesis according to which the tendency of an organization to juggle the logics of different fields (here academic and political) or to be absorbed in the logic of a single field modulates its willingness and capacity to adopt the identity of a think tank. Results suggest an association between a connection to the cultural category of the think tank and the ability of an organization to maintain, sometimes delicately, a dual commitment toward research and action without merging into either of these fields. They suggest that attention to the parameters of variation of these organizations may guide the formulation of more systematic sampling criteria. They also support the idea that the hybrid posture favoured by think tanks is of strategic significance for acting in different arenas of public policy.