  There has been a paradigm shift from the well-known laws of thermal radiation
derived over a century ago, valid only when the length scales involved are much
larger than the thermal wavelength (around 10 $\mu$m at room temperature), to a
general framework known as fluctuational electrodynamics that allows
calculations of radiative heat transfer for arbitrary sizes and length scales.
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 and/or directional selectivity. We introduce briefly the context and
the main steps that have led to the current boom of ideas and applications. We
then discuss the original and impactful works gathered in the associated
Special Topic collection, which provides an overview of the flourishing field
of nanoscale thermal radiation.
