The recent development of functional crystalline nanomaterials for therapeutics is described. In contrast to conventional therapeutic approaches, nanomaterial-based systems present novel therapeutic opportunities; for example, by allowing active agents to be site-specifically delivered and efficiently absorbed while offering fewer or reduced side effects. In addition, nanomaterials are generally amenable to surface functionalization and interior doping. These attributes provide the nanomaterials with tunable surface, optical, magnetic, thermal and mechanical properties that are important for applications ranging from controlled release of drugs to photothermal therapy. In this article, we seek to provide a conceptual framework for understanding nanomaterial-based therapeutics. We also attempt to highlight recent therapeutic applications involving some representative nanostructured materials. With improved control over the synthesis and functional characteristics of nanomaterials, the emergence of nanomaterial-based therapeutics will likely accelerate future medical research and improve patient care.