Because problem-based learning has come to mean so many different things, it is best to begin with a description. Rather than starting with content, PBL begins with a problem. Rather than posing problems with clear-cut, right answers, PBL presents students with less well-structure problems to which there are no single solutions. It is a learner-centered, not content- or instructor-centered approach. It challenges learners to become increasingly responsible for their own learning.