Among his many accomplishments in educational psychology, Merlin C. Wittrock is perhaps best remembered for his enduring contributions to the science of learning. His vision of how learning works is best explicated in articles published in "Educational Psychologist" (Wittrock, 1974, 1978, 1989, 1991, 1992), beginning with his classic 1974 article, "Learning as a Generative Process." In particular, Wittrock's contributions to the science of learning include (a) developing the generative theory of learning, (b) testing the generative theory of learning, and (c) applying the generative theory learning. In this article, I briefly summarize each of these accomplishments and describe how they influenced the field and my own research on learning and instruction.