This systematic review synthesizes and organizes existing research on teachers’ professional knowledge related to self-regulated learning (SRL) and its assessment. Although teachers play a central role in fostering and evaluating students’ SRL, the field lacks conceptual clarity regarding the types of knowledge required for these tasks. Drawing on established models of teacher professional competencies and knowledge, this review distinguishes three interrelated dimensions that together constitute the Teacher Knowledge of SRL (TK-SRL) framework: content knowledge of SRL (CK-SRL), pedagogical content knowledge for promoting SRL (PCK-SRL), and assessment knowledge for diagnosing SRL (AK-SRL). Across 33 included studies, substantial variability was evident in how teachers’ knowledge of SRL was conceptualized and operationalized. Definitions of SRL ranged from comprehensive theoretical accounts to broad, implicitly stated descriptions, thereby limiting comparability across studies. Methodological heterogeneity and the use of non-standardized assessment approaches further constrained the synthesis of findings. CK-SRL was by far the most frequently examined dimension, whereas PCK-SRL and, particularly, AK-SRL received considerably less empirical attention. Overall, the evidence suggests that teachers have partial, unevenly developed knowledge across all three dimensions, with limited and inconsistent associations between knowledge and other aspects of professional competence or instructional practice. These findings highlight the need for clearer, shared conceptualizations of SRL and more coherent, theory-driven approaches to assessing teachers’ knowledge of SRL. Building on this synthesis, we discuss implications for teacher education, propose directions for future research, and emphasize the importance of sustained professional development to strengthen all facets of teachers’ knowledge of SRL.