A "science of e-learning" involves the scientific investigation of how people learn in electronic learning environments. Three elements of a science of e-learning are: a) "evidence"--a base of replicated findings from rigorous and appropriate research studies; b) "theory"--a research-based theory of how people learn in electronic learning environments, which yields testable predictions; and c) "applications"--theory-based principles for how to design electronic learning environments, which themselves can be tested in research studies. This article provides examples of these three elements from a program of research on multimedia learning. (Contains 2 tables and 1 figure.)