Our goal in this chapter is to showcase the various theories and cognitive models that have been developed by mathematics and statistics educators regarding the development of probabilistic thinking from a "practitional" perspective. This perspective juxtaposes the work of mathematics and statistics educators with research on probability from the field of psychology. Next, we synthesize theories and models that have been developed for specific probability concepts and processes. These models suggest different levels or patterns of growth in probabilistic reasoning. Finally, we examine the role these models have had on instruction and curriculum recommendations.