In this article, I offer a pragmatist conceptual framework to link the sociology of health and illness with the sociology of science and technology. Starting from an examination of the practice of doing medicine and science, I extend Anselm Strauss's trajectory concept to analyze the temporality and processual character of an evolving phenomenon in two important ways. First, I analyze how a single trajectory emerges out of the interaction of multiple trajectories and how emerging and existing trajectories shape each other with differential power. Second, in accord with recent writings in science and technology studies, agency is extended from humans to non-humans. I discuss different origin and ending strategies of trajectories and the management of trajectories over time.