This volume of Annual Review of Heat Transfer (ARHT) covers micro/nanoscale thermal radiation, which concerns both near-field radiative heat transfer between closely spaced objects and the interaction of electromagnetic waves with micro/nanostructured materials that modifies the far-field radiative properties. It covers both experimental techniques and computational methods in near-field radiative transfer, including the basic principles, methodology, historic aspects, and applications. Various approaches that use metasurfaces/metamaterials such as photonic crystals, gratings, embedded nanoparticles, phase change materials, and graphene and other 2D materials to control the wavelength selectivity, angular and polarization dependence, and temperature effects are extensively reviewed. These studies have enormous applications in photonic and optoelectronic devices, solar cells and solar absorbers, thermophotovoltaic devices, optical filters, and noncontact temperature measurement. ARHT, Volume XXIII will benefit researchers interested in this emerging and rapidly developing field for future scientific discoveries and real-world applications.