Decades of research document underperformance of Latino/a youth in mathematics, yet little is known about the day-to-day mathematics socialization of Latino/a youth. This research used qualitative case studies of two Algebra 1 classrooms and seven Latino/a focal students to document and describe two major influences on Latino/a youths' mathematics identities: their individual beliefs and their negotiation of identity in classroom settings. I proposed a three-tiered framework for mathematics identity drawing on students' self-concepts, sociocultural learning theory, and Critical Race Theory (CRT) to research the perspectives Latino/a students had about their own mathematics identities. This study focused on how Latino/a students described the role of language and race in learning mathematics, how Latino/a youth exhibited agency in their mathematics educations, and the role of different features of mathematics classrooms in negotiating their mathematics identities. Findings from students' perspectives suggest racial identity plays a role in the mathematics identity negotiation for Latino/a students in complex ways. Some students readily named stereotypes around Asian students as being high achieving, and then positioned Latino/as as lower achieving. Linguistic identity played a key role in how one pair of focal students in each classroom engaged in strategic partnerships and how they displayed agency--for one student in her own mathematics identity, and for the other student in an attempt to help her partner learn algebra. The findings from the classroom analysis suggest that attending to multiple aspects of classroom practice can provide insight into how Latino/a youth negotiate their mathematics identities in classrooms, and that the proposed aspects of classroom practice may be a useful analytic framework for classroom research. The findings contribute to important dimensions to attend to in the mathematics identity development and classroom socialization experiences of Latino/a youth, and highlight the potential value of CRT in research on mathematics identity. The frameworks proposed could contribute to equity projects focused on the experiences of Latino/a youth and youth from other communities historically marginalized by schooling. [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.]