This chapter describes empirical findings associated with the expertise reversal principle, its interpretation within cognitive load theory, conditions of applicability of the principle, and its implications for research and instructional design. Cognitive science studies of differences between experts and novices have demonstrated that the knowledge base held in long-term memory is the most critical characteristic of competent performance in any subject area. It reviews empirical studies supporting the expertise reversal principle and shows that this principle has a plausible theoretical explanation within a cognitive load framework. An essential future research direction is that of identifying instructional designs and procedures that are optimal for different levels of learner expertise. Adaptive multimedia systems that tailor instructional methods to levels of learner expertise have the best potential for optimizing cognitive load in multimedia learning. Rapid diagnostic assessment tools could potentially be used as real-time measures of expertise for adaptive fading procedures.