Crucial in any learning process are the activities that learners undertake: reading, thinking, discussing, exploring, problem solving, etc. When learners are passive you cannot expect them to learn much. The primary role of any instructional agent, whether it is a teacher, the learners themselves or a computer, is to stimulate the performance of learning activities that will gradually result in the attainment of the learning objectives. The instructional agent defines the tasks, provides the contexts and resources to perform the tasks, supports the learner during task performance and provides feedback about the results. The learning activities that are needed to obtain some learning objectives are in most cases carefully sequenced according to some pedagogical principles. This sequence of learning activities that learners undertake to attain some learning objectives, including the resources and support mechanisms required to help learners to complete these activities, is called a learning design.