This chapter provides background information on the meaning and implications of the terms motivation, engagement, and interest for learning science research and practice. Working definitions and findings from study of these variables are overviewed, and methods are described. Case material is provided for purposes of illustration. It is argued that motivation, engagement, and interest are central to deeper learning, and that overlooking their centrality in individuals’ participation and learning could affect whether a project’s goals will be achieved, and/or whether a research project is likely to inform practice. Three design principles are proposed. In brief, learners: (1) need to work with disciplinary content in order for it to become rewarding; and on the basis of their present phase of interest development may need (2) different types of support to meaningfully engage and (3) the structure of tasks, activities, and/or the learning environment to be adjusted.