In this discussion paper, teaching and learning are characterized as being situated, complex, and reciprocally interactive activities. Accordingly, a teacher's pedagogical actions are always action and reaction at the same time. Irrespective of the reciprocally interactive nature of teaching and learning, educational research has sought to identify characteristics of teacher expertise that enable teachers to influence students' learning in a systematic and positive way. In this respect, the contributions to this special issue offer an innovative research paradigm, because they bring together different and originally separated strands of research: (1) research on professional vision in teacher education, (2) research on the structure and development of expertise in cognitive science, (3) research on cognitive processes by means of eye-tracking technologies in psychology, and (4) research on educational effectiveness and instructional quality in educational science. Following this introduction, a detailed discussion of the rewards and challenges of each of the seven contributions is provided. This discussion leads to the following conclusions: (a) The emphasis on the "reacting teacher" in professional vision research undervalues the role of lesson planning for the flexible handling of sudden events during class instruction. (b) The assumption of professional vision as "mediator" between a teacher's knowledge and pedagogical actions overlooks that teachers can sometimes do more than they can tell. (c) Not all of the gaze behavior that is currently studied needs to be instructed. (d) Research should move beyond explorative expert-novice comparisons to hypotheses-driven designs that investigate how teachers can learn to successfully apply evidence-based pedagogical principles.