Autoimmune diseases, rejection of transplanted organs and grafts, chronic inflammatory diseases, and immune‐mediated rejection of biologic drugs impact a large number of people across the globe. New understanding of immune function is revealing exciting opportunities to help tackle these challenges by harnessing—or correcting—the specificity of immune function. However, realizing this potential requires precision control over the interaction between regulatory immune cues, antigens attacked during inflammation, and the tissues where these processes occur. Engineered materials—such as polymeric and lipid particles, scaffolds, and inorganic materials—offer powerful features that can help to selectively regulate immune function during disease without compromising healthy immune functions. This review highlights some of the exciting developments to leverage biomaterials as carriers, depots, scaffolds—and even as agents with intrinsic immunomodulatory features—to promote immunological tolerance.