Students come to CS from a variety of backgrounds and with a variety of preconceptions. Some initially select CS with a very vague idea of the field they are majoring in. In this paper, I describe CS undergraduates' view of the field of Computer Science. The approach was qualitative and cognitive: I studied what students think CS is and how students reasoned about their courses and curriculum. Through the use of grounded theory in 37 qualitative interviews with students and student advisors, I extracted three different conceptions about CS found in undergraduate CS majors using Grounded Theory. Overall, students had reasonable views of CS at a high level but lacked specifics. Students had difficulty describing subfields of CS or anticipating the content of courses they selected.