In this project I study introductory undergraduate physics classrooms as critical sites in the development of students’ relationships with physics. Drawing on interviews with students, observations of classrooms, and analyses of textbooks, I compare introductory undergraduate courses in physics required for engineering majors, physics majors, and students in the life sciences, respectively to understand the ways that students in each class come to understand themselves as physics learners. Some of the students whose stories I will attempt to capture are learning to think like physicists, some are learning to incorporate physics into their engineering work and method, some are learning what role physics might play in their lives if they will be neither physicists nor engineers. All of these relationships depend on particular assumptions about what it means to become a physicist, or an engineer, or a biologist, or a non-scientist. In short, they are all thoroughly intertwined with identity. What I want to understand about learning physics is what it has to do with identity--how it participates in the fashioning of different kinds of student selves, and how in turn those student identities participate in defining and maintaining the disciplinary identity of physics.