  5G radio at millimeter wave (mmWave) and beyond 5G concepts at 0.1-1 THz can
exploit angle and delay measurements for localization, by the virtue of
increased bandwidth and large antenna arrays but are limited in terms of
blockage caused by obstacles. Reconfigurable intelligent surfaces (RISs) are
seen as a transformative technology that can control the physical propagation
environment in which they are embedded by passively reflecting EM waves in
preferred directions. Whereas such RISs have been mainly intended for
communication purposes, RISs can have great benefits in terms of performance,
energy consumption, and cost for localization and mapping. These benefits as
well as associated challenges are the main topics of this paper.
