The ability to control thermal radiation is important for a broad range of applications, including thermal management, spectroscopy, optoelectronics, and energy-conversion devices. Nanostructured materials, such as metamaterials and photonic architectures, offer new opportunities for shaping the infrared thermal spectrum and improving the performance of thermal devices. In addition, there has been a paradigm shift from the familiar laws of thermal radiation derived over a century ago, valid only when the involved length scales are much larger than the thermal wavelength (around 10 µm at room temperature), to a general framework known as fluctuational electrodynamics that allows calculations of radiative heat transfer for arbitrary sizes and distances. Near-field radiative heat transfer and thermal emission in systems of sub-wavelength size can exhibit super-Planckian behaviour, i.e. flux rates several orders of magnitude larger than that predicted by the Stefan–Boltzmann (or blackbody) limit. These effects can be combined with novel materials, e.g. low-dimensional or topological systems, to yield even larger modifications and spectral selectivity. The goal of this Special Topic Collection is to provide an overview of the flourishing field of nanoscale thermal radiation and its key applications, gathering original and impactful works.