The purpose of this study was to investigate the phenomenon of the ways in which Black undergraduate students, majoring in mathematics intensive disciplines, at the University of Virginia construct mathematics achievement identities. Specifically, this study sought to identify and examine factors that impacted these students' identity construction and to determine how those factors operated to influence that construction. This study was guided by situated-mediated identity theory (SMIT). The research tradition chosen to accomplish the goals of this study was phenomenology. There were three research questions I sought to answer with this study: (1) What are the mathematics educational experiences of Black students majoring in mathematics-intensive disciplines at the University of Virginia; (2) What aspects of their experiences served to mediate the constructions of mathematics achievement identities; and (3) How do these mediating factors operate to influence the construction of mathematics achievement identities? In response to the first research question, the following three assertions were deduced from the data collected: (1) Black students change their definitions of success in mathematics over time. As mathematics becomes more advanced and as the learning environment changes, success is viewed through the lens of competency as opposed to grades; (2) Black students become increasingly aware of race and its implications through various experiences. Over time, these students began to negotiate who they are to others based on these experiences; (3) Black students often experience isolation in mathematics classrooms and other mathematics learning environments. In addition to highlighting the mathematics educational experiences of Black students, these assertions also expanded the discussion related to the second research question. To that end, I suggest experiences with mathematics, race and stereotypes, and within learning space act together as mediators of mathematics achievement identities of the students in this study. To address the third question, descriptions of each student's mathematics achievement identity were constructed through analysis of the data. These descriptions emphasize positive and negative aspects of each student's experience, such as mathematics success and self-efficacy, feelings of isolation, and perceptions of stereotypes. [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.]