This chapter reports on the development of a taxonomy of didactic problems used in problem-based learning (PBL) curricula. It distinguishes four categories of knowledge acquired by students in the course of their PBL training: explanatory, descriptive, procedural, and normative knowledge. In response to the need for students to acquire these kinds of knowledge relevant to their discipline, and because problems are the main instruments through which the learning process is directed in PBL curricula, teachers develop any of four types of problems: explanation problems, fact-finding problems, strategy problems, and moral dilemma resolution problems. The purpose of the taxonomy is to describe sufficiently and exhaustively the variety of problems found in PBL curricula. Thus, each of these kinds of problems matches one type of knowledge. A taxonomy such as this may help teachers to design appropriate problems for PBL, and it may guide students in their choice of learning strategy.