Skill Acquisition Theory accounts for how people progress in learning a variety of skills, from initial learning to advanced proficiency. The scientific roots of Skill Acquisition Theory are to be found in various branches of psychology, but this research area has proven to be remarkably resilient through various developments in psychology, from behaviorism to cognitivism to connectionism. The same can be said about other directions in which skill acquisition research has expanded in recent years: the study of the forgetting of skills and the role of distributed versus massed practice in learning and forgetting. The acquisition of declarative knowledge of a kind that can be proceduralized requires the judicious use of rules and examples. Furthermore, research on skill acquisition, whether carried out with behavioral data or through neuroimaging or computer modeling, is tremendously explicit in its procedures and claims.