Few question the value of teacher-student relationships (TSRs) for educational outcomes. TSRs are positively associated with students' achievement and engagement, as well as teachers' well-being. Building and maintaining these crucial classroom relationships, however, is not easy. Drawing on prominent motivation theories in educational psychology, I present the Motivating Teacher-Student Relationships framework for understanding what motivates teachers to build positive TSRs. In particular, I focus on how teachers' motivational beliefs about TSRs energize, direct, and sustain their efforts to engage in relationship-building behaviors and, thus, lead to positive relationships with their students. To build positive TSRs, teachers must believe it is their role to build TSRs, value TSRs, and believe they can successfully build TSRs (i.e., have relational self-efficacy). These beliefs are shaped by teachers' sociocultural contexts and can facilitate or undermine the development of these learning relationships. With a greater understanding of how motivational beliefs influence social relationships, the field of education can more effectively develop theoretically grounded interventions to improve TSRs and mitigate inequality.