The capacity limitations of working memory are a major impediment when students are required to learn new material. Furthermore, those limitations are relatively inflexible. Nevertheless, there is one technique that can effectively expand working memory capacity. Under certain well-defined conditions, presenting some information in visual mode and other information in auditory mode can expand effective working memory capacity and so reduce the effects of an excessive cognitive load. This effect is called the modality effect or modality principle. It is an instructional principle that can substantially increase learning. This chapter discusses the theory and data that underpin the principle and the instructional implications that flow from the principle.