One essential piece of implementing of PBL is the problem. There have been calls from practitioners in the PBL field for a systematic process for designing effective PBL problems. Yet, the research efforts to explore, develop, and test PBL problem design methods or processes are still sparse. From an instructional designer and researcher's perspective, I deem problem design to be the first step to ensure not only the proper affordance of the learning goal but also the students' overall learning process in PBL implementation. PBL problem design is the area I have studied most consistently and passionately. In this paper, I share my continuing study of PBL problem design, from the original 3C3R model and the 9-step design process, to an examination of the cognitive components of PBL problems such as problem difficulty structure and levels, to my recent focus on the affective components of PBL problems.