In support of the thesis stated above, this article will provide a definition of media and use it to examine the theoretical and research literature on learning from books, television, computers, and multimedia environments. Each section will examine how the complementary construction of representations, and operations performed on them, is influenced by characteristics of the medium, designs that take advantage of these, and the characteristics of learners and tasks. The intent is to demonstrate the relative cognitive effects of learning with different media, particularly effects related to the structure, formation, and modification of mental models.