There is a need for research to explore the connections between students' self-perceptions and their goals and future engagement with mathematics. This is particularly the case when considering that student interest declines as they transition through K-12 and gender differences continue to persist in mathematics related careers. Knowing how students identify with mathematics might provide insight into students' self-perceptions of mathematics and how these perceptions relate to students' career choices. This quantitative study uses a mathematics identity framework based upon students' self-perceptions related to mathematics. Specifically, students' self-perceptions relating to mathematics interest, recognition by others in mathematics, and mathematical competence and performance were explored. Data were drawn from the Factors Influencing College Success in Mathematics (FICS-Math) project, which was a national survey of college students enrolled in a single-variable calculus course at 2- and 4- year institutions across the United States. This survey yielded a total of 10,492 surveys from students attending 336 college calculus courses/sections at 134 institutions. The results highlight the salience of the mathematics identity framework, indicating that mathematics interest, being recognized by others in mathematics, and beliefs about their ability to perform and understand mathematics were directly related to students' mathematics identity. This led to the construction of a structural equation model for the mathematics identity framework detailing the relationship between the sub-constructs of mathematics identity. Results also indicated that gender differences in students' self-perceptions still exist though effect sizes were small. In addition, self-perceptions as seen through a mathematics identity proxy were shown to be a strong predictor of students' career choice as a mathematician, as a science/math teacher, and in STEM fields. This study establishes an explanatory framework for mathematics identity that provides insight into gender differences and students' career choices in mathematics related fields. Implications of this study are that students' self-perceptions might provide insight into why students persist in areas related to mathematics, how teachers might help students develop a positive sense of affiliation with mathematics, and how this mathematics identity framework might provide a lens for future research. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]