The purpose of this article is to clarify conceptions, definitions, and applications of learning and problem-solving efficiency. Conceptions of efficiency vary within the field of educational psychology, and there is little consensus as to how to define, measure, and interpret the efficiency construct. We compare three diverse models that differ in computation (i.e., how efficiency scores are calculated), measurement (i.e., what variables are used to calculate an efficiency score), and application (i.e., under what research and instructional contexts each model should be used). Strengths and weaknesses of each model are discussed. The article provides a definition of the underlying construct assessed by each model and considers the most plausible interpretation of each type of efficiency score. Recommendations are provided for using these conceptions in future research, and especially the use of multiple measures in the same study. (Contains 2 tables.)