Richard Mayer argues that few of the many strong claims made for the transformative potential of new technologies have been convincingly tested against research evidence. A major reason is that too often a "technology-centred", as opposed to a "learningcentred", approach is followed. A convincing theory of how people learn with technology can be based on three important principles: "dual channels" (people process sound and visual images separately), "limited capacity" (people can only process a small amount of sound or image at a time), and "active processing" (meaningful learning depends on engagement in appropriate cognitive processing). These are explained and applied to argue that effective instruction with technology helps cognitive processing in learners without overloading their cognitive system; this can be achieved by reducing extraneous processing, managing essential processing, and fostering generative processing. How this can be done applying different techniques and principles, together with supportive evidence, are presented in detail.