The articles in this special issue represent the findings of researchers working in classroom settings to explore key issues in learning through problem solving. Although they vary in the domains being studied, the age of students, and the methods they employ, there are numerous common themes that can inform both theory and practice. The authors have grappled with the complex task of putting problem-based curricula into practice. They report here the difficulties they faced, the factors contributing to their successes, and the lessons they have learned.