Publisher This chapter discusses various issues in which the basic method of comparing expert to novice performers is applied across a wide range of skills and situations. These issues arise from the application of an approach developed to study the nature of expertise in cognitive tasks to motor tasks. In most cases where speeded motor responses are required (musical performance, human speech, or video game controller manipulation) reaction and movement time do not appear to constrain skilled performance. Another controversy that surrounds expert performance is that task specific sensory information is handled differently by someone once they become skilled. This is one area where traditional motor learning and expert—novice research could benefit by amalgamating paradigms. The most common distinction in the motor literature and one still very much of value is the difference between open and closed skills. Another controversy in the assessment of expertise is how much of expert behavior can be explained by experience and training versus how much by individual abilities the subject brings to the task. Another problem in discussing expertise is that within any one expert, skill, and experience are inherently confounded. Consistency of performance is critical in assessing whether someone is an expert. A final issue in the study of motor expertise is that protocol analysis is an appropriate methodology for the elaboration of procedural skills.