The research in Physics Education has to do with the search of solutions to the complex problem of how to improve the learning and teaching of physics. The complexity of the problem lies in the different fields of knowledge that need to be considered in the research. In fact, besides the disciplinary knowledge in physics (which must be considered from the conceptual, the historical, and the epistemological framework), one has to take into account some basic knowledge in the context of psychology and the cognitive sciences (for the general and contextual aspects of learning) and some basic knowledge in education and comunication (for what concerns teaching skills and strategies). Looking back at the historical development of the research one may recognize that the complexity of the endeavour was not clear at first but became clear in its development, which shifted the focus of the research in the course of time from physics to learning to teaching. We may say that the research started, more than 30 years ago, with a focus on disciplinary knowledge. Physicists in different parts of the western world, after research work in some field of physics, decided to concentrate on the didactical comunication of physical knowledge.