Can multimedia learning environments be designed to foster positive emotions that will improve learning and related affective outcomes? College students (N = 118) were randomly assigned to 4 conditions created by 2 factors related to learners' emotion: "external mood induction" (positive vs. neutral emotions) and "emotional design induction" (positive vs. neutral emotions). A computer-based lesson on the topic of immunization was used as multimedia learning material. Results indicate that applying emotional design principles to learning materials can induce positive emotions and that positive emotions in multimedia-based learning facilitate cognitive processes and learning. Controlling for the germane load of the materials, the internal induction of positive emotions through design of the materials increased comprehension and transfer, whereas the external induction of positive emotions through mood induction enhanced transfer but not comprehension. Positive emotions induced through mood induction significantly increased the amount of learners' reported mental effort, whereas positive emotional design reduced the perceived difficulty of the learning task. Positive emotions increased motivation, satisfaction, and perception toward the materials. Mediation analyses suggest that the effect of positive emotions induced externally was mediated by both motivation and mental effort but found no mediators for emotion induced via emotional design, suggesting that positive emotional design has a more direct impact on learning than externally induced emotions. The study suggests that emotions should be considered an important factor in the design of multimedia learning materials. (Contains 2 figures and 2 tables.)