Positive relationships between teachers and students are one of the most crucial but also most complex determinants of successful teaching and learning processes. In the last few decades, many attempts have been made to conceptualize teacher-student relationships (TSR) in theoretical models. Until now, however, a precise definition of TSR as well as a comprehensive model distinguishing between teacher-student interactions and relationships, including all agents involved (teachers, students, and classes), and considering the reciprocal interplay of (perceived) behaviors, intrapsychological characteristics, and contextual factors related to TSR are still missing. Hence, in this conceptual work, we first establish a definition of TSR. Then, we provide an overview of existing theoretical models and—building on this overview—propose a new comprehensive model that both integrates and extends previous TSR models within the school context, aiming to guide prospective research. Finally, we identify key challenges and directions for future research.