"We must explain why science — our surest example of sound knowledge — progresses as it does, and we must first find out how in fact it does progress" (Kuhn, 1970, p. 20). Many answers have been proposed to these two questions. In choosing to organize this chapter in terms of different models of scientific development, I have deliberately sought to emphasize the collective character of work in science studies. My aim is to avoid the repetitive and controversial step of taking a few selected books by a number of great authors — the science studies canon — as the point of departure. To be sure, my way of presenting the arguments has its drawbacks. For instance, the debates that have driven the field as it has grown do not come into focus. However, the theoretical structure of arguments and choices is made clearer, as is the fact that analysts are always struggling with a series of different dimensions. It is thus impossible to give a definition of, for example, the nature of scientific activity, without at the same time suggesting a certain interpretation of the overall dynamics of development and establishing the identity of the actors involved. Even the most philosophical works imply a conception of the social organization of science, and reciprocally the purest sociological analyses assume views of the nature of scientific knowledge.