Contemporary research in science education has promoted learning of content and reasoning practices through inquiry. This chapter sketches a theory of epistemic design, focusing on design for science classes. It has the practice-based goal of explicating instructional principles of design that can promote such epistemic growth. The chapter provides a brief overview of our model-based inquiry project, called Promoting Reasoning and Conceptual Change In Science (PRACCIS); this provides needed background for later discussions. It explicates the components of the AIR model that are most relevant to our epistemic design work and discusses the implications of each component of the AIR model for epistemic design. Finally, the chapter summarizes and highlights several design features that are hallmarks of PRACCIS and why they are expected to promote epistemic growth that can transfer spontaneously to new settings. A Model-Evidence Link (MEL) matrices are thus designed both to promote a reliable, systematic, process for creatively coordinating theories and evidence.