This book explores a particular instructional strategy to foster mathematics learning, namely Problem-centered learning. In the 21st century there is an urgent need for our students to know mathematics in a way that is fundamentally different from how many in the twentieth century experienced mathematics. If they are to enrich their own lives and the society in which they live students need to know not just facts and procedures, but how to think mathematically, to interpret their world through a mathematical lens (among other lenses). To do this they need to experience mathematics learning as a sense making activity, as an activity of constructing patterns and relationships. In this book Grayson Wheatley and a group of his former doctoral students and colleagues will elaborate PCL as an approach that fosters such learning in the mathematics classroom. The topics discussed should be of interest to researchers, school administrators, and professionals in the field.