Teachers differ substantially in their instructional performance in the classroom. Thus, researchers and policymakers are interested in how these differences can be explained and how the instruction provided by low-performing teachers can be improved. Previous research has focused either on generic (cognitive ability and personality) or profession-specific (professional knowledge, beliefs, and motivation for teaching) teacher characteristics as predictors of instructional quality but their relative importance has not yet been tested.Hardly any studies have combined central generic and profession-specific variables in ascertaining their relative importance for instructional quality. In the present study, we seek to close this research gap.We investigated 209 German mathematics teachers and their 4,672 students attending grades 7-10 (13- to 16-year-old students).Teacher characteristics (cognitive ability, personality, professional knowledge, beliefs about, and enthusiasm for teaching) were assessed using standardized tests and self-report measures. Instructional quality (learning support, classroom disruptions, and cognitive activation) was rated by the students.Using structural equation modelling, we found extraversion, enthusiasm for teaching, and pedagogical/psychological knowledge to be significant predictors of learning support (R  = .31) and conscientiousness and enthusiasm for teaching to be significant predictors of classroom discipline (R  = .21). We did not find significant predictors for cognitive activation.Our results indicate the relative significance of generic and profession-specific teacher variables for instructional quality. Overall, a substantial amount of variance in instructional quality is explained by teacher characteristics.