A material’s properties are derived from its constituent material composition and its structural hierarchy across length scales down to the nanometer level. At submicron length scales, materials exhibit unique size-affected mechanical properties such as enhanced strength, ductility, and flaw tolerance, but these are generally lost in bulk materials. Emerging fabrication methods have enabled the creation of materials with controllable architectures down to the nanoscale. These micro- and nanoarchitected materials utilize both resilient architectures and size-affected constituent materials to achieve unprecedented mechanical properties such as ultrahigh strength at low density, recoverability after large applied strains in intrinsically brittle materials, and metamaterial properties such as chirality and negative static compressibility. In this article, we describe the governing principles behind these materials and outline recent progress in the field. We unravel the details of the deformation and failure processes to facilitate a fundamental understanding of effective materials properties and provide a guideline for the design of the next generation of nanoarchitected materials.