This critical literature review documents the shifts and variations in Case-Based Reasoning (CBR) terminology and reasoning models that have arisen in the past twenty years. Different versions of CBR theory, differences in terminology across these versions, and shifts in terminology within individual programs of theory development and research in CBR are identified. A framework for understanding the shifts and variations in CBR literature, and a framework for categorizing the variations in CBR cognitive science literature are proposed. Finally, educational applications of CBR are examined within the context and framework for understanding CBR I developed, and possible variations of these applications are explored.