Physics Education Research (PER) combines the application of fundamental knowledge about learning and the discipline specific knowledge of physics to investigate ways of making the teaching and learning of physics more effective and efficient, primarily at the university level. It is an interdisciplinary area with roots in the core disciplines of Physics, Education, and Cognitive Science. The focus of the Minnesota physics education group is the investigation of student difficulties with problem solving in the context of physics. We apply our results to develop practical curricular materials and techniques that can be used by physics instructors and students. The group also develops research methodology and measuring instruments to further the goals of PER.