Suppose you want to design (or select) (a) a computerbased training program to teach employees how to use a new database program, (b) a biology textbook for high school students, (c) an instructional video game aimed at promoting healthy eating, or even (d) a PowerPoint presentation on a topic in educational psychology. Each of these is an example of what I call a multimedia instructional message-a lesson containing words (e.g., printed words or spoken words) and pictures (e,g., illustrations, photos, animation, or video) that is intended to foster learning. How would you decide the best way to present your multimedia instruction? To help answer this question, you need some way of judging whether a proposed instructional method is consistent with research-based theories of how people learn (i.e., the science of learning) and evidence-based principles of how to design instruction (i.e., the science of instruction).Let's consider three approaches to the relation between theory and practice (Mayer, 1992). In the one-way street approach, psychologists develop a theory of how people learn that is based on research, and educators apply the theory in their lessons. The problem with the one-way street approach is that a clear specification of how people learn does not automatically yield a clear specification of effective instructional methods and materials. In the dead end street approach, psychologists busy themselves in building a theory of learning that is not closely related to authentic educational challenges-such as studying how laboratory animals run mazes or how adults memorize word lists-while educators seek research that determines the best method of instruction without regard to how or why it works. Finally, in the two-way street approach, there is a reciprocal relation between learning theory and educational practice in which the science of learning must be expanded to be able to explain how learning works in authentic learning situations, and the science of instruction must be expanded to consider the conditions for each instructional principle based on an understanding of how the human mind works. Figure 1 summarizes the relation between basic research-which has been attributed to the science of learning (SOL)-and applied research--which has been attributed to the science of instruction (SOI). A defining feature of the science of instruction is a focus on authentic learning situations rather than contrived learning situations, so Figure 1 shows "SOI" in the two quadrants on the right. A defining feature of the science of learning is a focus on testing learning theory, so "SOL" is shown in the two quadrants at the bottom of the figure. The four quadrants in Figure 1 are inspired by the work of Stokes (1997). The top left quadrant-conducting nontheoretical studies on contrived learning situations-is consistent with neither the SOL nor the SOI and is unlikely to yield information that is helpful for theory or practice. The top right quadrantconducting nontheoretical studies on authentic tasks-is consistent w...