To summarize this Introduction, future students will develop competencies in their domain of study by working on rich learning tasks in multimedia learning environments where assessments will be based on their complex performances (see also Kirschner, van Vilsteren, Hummel, & Wigman, 1996). The next three sections discuss the main instructional design questions that must be answered in order to be able to develop such environments: (1) how to design realistic learning tasks for complex learning to occur?, (2) how to deliver such tasks and resources in multimedia environments?, and (3) how to diagnose learners' progress on the basis of their complex task performances?