Positive teacher-student relationships are critical for motivation in secondary school yet are conceptualized and measured inconsistently in motivation research. Motivation studies that draw on relational theories typically treat teacher-student relationships as a multidimensional construct, comprising positive (e.g., closeness) and negative (e.g., conflict) dimensions. In contrast, studies drawing on motivation theories typically use unidimensional relationship measures (e.g., only closeness). Studies also differ in their measures of teacher-student relationships and in whether they study dyads ("my teacher to me") or broader groups ("teachers to me"; "my teacher to us"), and it is unclear which approaches are most common in current adolescent motivation research and how they have shaped current understandings of relationships in the field. Given this confusion, the aim of our systematic review was to map how teacher-student relationships have been conceptualized, measured, and analyzed in adolescent motivation research published between 2010 and 2023. Using PRISMA guidelines, 237 studies and 222 unique relationship measures were identified. The findings showed that teacher-student relationships and teacher support were used interchangeably across studies, both in terms of terminology and measurement. Most studies also examined teacher-student relationships using unidimensional measures, rather than multidimensional, with dyadic and non-dyadic relationships both common. Finally, there was no clear pattern of conceptualization or measurement for specific motivation constructs. These findings raise concerns regarding alignment between theorizing and measurement of teacher-student relationships in motivation research. We offer a path forward for identifying and appropriately using existing measures of teacher-student relationships vs support, as well as highlight the need for the development of measures which critically engage with conceptual concerns regarding teacher-student relationships and which reflect an integrated understanding of core relationship components (e.g., dyadic, multidimensional) identified across relational and motivation theories.