This dissertation takes a qualitative look at the understanding of mathematical statements and proofs held by college students enrolled in a transitional course, a course designed to teach students how to write proofs in mathematics. I address the following three research questions: (1) What are students' understandings of the structure of mathematical statements? (2) What are students' understandings of the structure of mathematical proofs? (3) What concerns with the nature of proof do students express when writing proofs? Three individual interviews were held with each of the six participants of the study during the final month of the semester. The first interview was used to gain information about the students' mathematical backgrounds and their thoughts and beliefs about mathematics and proofs. The second and third interviews were task-based, in which the students were asked to write and evaluate proofs. In this dissertation, I document the students' attempts and verbal thoughts while proving mathematical statements and evaluating proofs. The results of this study show that the students often had difficulties interpreting conditional statements and quantified statements of the form, "There exists...for all..." These students also struggled with understanding the structure of proofs by contradiction and induction proofs. Symbolic logic, however, appeared to be a useful tool for interpreting statements and proof structures for those students who chose to use it. When writing proofs, the students tended to emphasize the need for symbolic manipulation. Furthermore, these students expressed concerns with what needs to be justified within a proof, what amount of justification is needed, and the role personal conviction plays within formal mathematical proof. I conclude with a discussion connecting these students' difficulties and concerns with the social nature of mathematical proof by extending the theoretical framework of the Emergent Perspective (Cobb & Yackel, 1996) to also include social norms, sociomathematical norms, and the mathematical practices of the mathematics community
