Advances in growth mindset scholarship now recognize the role of instructors' mindsets in shaping classroom mindset culture. In the present paper, we synthesize the newly developing instructor mindset literature and report on a dataset that includes student (N = 765) and instructor (N = 44) reports of instructor mindset beliefs and behaviors. We organize our paper around four key questions: (1) What teaching behaviors signal instructors' mindset beliefs to students? (2) What teaching behaviors are associated with instructors' mindset beliefs? (3) Do students and instructors in the same classroom agree about instructors' beliefs and behaviors? (4) Where should researchers target interventions aimed at promoting growth mindset cultures? We then discuss three problems that instructors might encounter when trying to create growth mindset cultures--when instructors inconsistently engage in growth mindset behaviors, when instructors unwittingly communicate a fixed mindset to students, and when students fail to notice instructors' growth mindset behaviors--and potential solutions to these problems. We end with implications for instructor-focused interventions, which include both encouraging instructors to engage in growth-focused behaviors and to state clearly why their behaviors communicate a belief in student growth.