Taking a Vygotskian sociocultural stance, this book demonstrates the meaningful role that L2 teacher educators and L2 teacher education play in the professional development of L2 teachers through systematic, intentional, goal-directed, theorized L2 teacher education pedagogy. The message is resoundingly clear: Teacher education matters! It empirically documents the ways in which engagement in the practices of L2 teacher education shape how teachers come to think about and enact their teaching within the sociocultural contexts of their learning-to-teach experiences. Providing an insider’s look at L2 teacher education pedagogy, it offers a close up look at teacher educators who are skilled at moving L2 teachers toward more theoretically and pedagogically sound instructional practices and greater levels of professional expertise. First, the theoretical foundation and educational rationale for exploring what happens inside the practices of L2 teacher education are established. These theoretical concepts are then used to conduct microgenetic analyses of the moment-to-moment, asynchronous, and at-a-distance dialogic interactions that take place in five distinct but sometimes overlapping practices that the authors have designed, repeatedly implemented, and subsequently collected data on in their own L2 teacher education programs. Responsive mediation is positioned as the nexus of mindful L2 teacher education and proposed as a psychological tool for teacher educators to both examine and inform the ways in which they design, enact, and assess the consequences of their own L2 teacher education pedagogy.