University mathematics classrooms are continuing to become more linguistically and culturally diverse. Students in these courses bring rich language resources for learning and engaging in classroom mathematical practices. Despite this diversity, little research has examined the role of language in post-secondary mathematics education. Using mixed methodologies, this dissertation focuses on exploring the learning experiences of multilingual students in undergraduate math courses, particularly in courses that use talk-intensive pedagogies like active learning. This research, informed by sociopolitical theory, frames language as a resource for student learning, while also recognizing the interconnectedness of language, power, and identity in the classroom. The data for this study stems from individual interviews with 28 multilingual undergraduate students and survey data from 464 students enrolled in introductory college math courses. Using a three-article format, each paper in this dissertation explores a different component of the research objectives. The first paper qualitatively examines the role of language in the undergraduate mathematics classroom, using a language-as-resource, language-as-political framework. The second paper uses qualitative methods to explore multilingual students' experiences engaging in active learning, and the student positioning that unfolded during group interactions with peers. The final paper presents a quantitative analysis of the relationship(s) between active learning pedagogies, students' identities, including their language identity, and students' experiences in undergraduate math courses. Across the three papers, this work helps capture the nuances and tensions that are often present in linguistically diverse undergraduate mathematics courses. The findings in this dissertation demonstrate the relevance of language in multilingual students' learning experiences and provide several implications for teaching in language diverse undergraduate mathematics courses. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]