The focus of this special issue is on the cognitive load underlying processes of interactive knowledge construction in a wide range of instructional multimedia platforms. Multimedia comprehension involves the parallel processing of auditory-verbal and visual-pictorial channels within working memory. By means of integrating multimodal information, students are able to acquire new knowledge. However, the processes of knowledge construction may be dependent on the load a task imposes on the learner's cognitive system. Such cognitive load is determined by prior knowledge, motivation, and processing strategies on the part of the learner as well as on task demands. Other critical factors that should be explored are goal adoption and perspective taking, effects of interactive animation, environmental support, and possibilities of collaboration. (Contains 2 figures.)