  Reconfigurable intelligent surfaces (RISs) have tremendous potential for both
communication and localization. While communication benefits are now
well-understood, the breakthrough nature of the technology may well lie in its
capability to provide location estimates when conventional approaches fail,
(e.g., due to insufficient available infrastructure). A limited number of
example scenarios have been identified, but an overview of possible RIS-enabled
localization scenarios is still missing from the literature. In this article,
we present such an overview and extend localization to include even user
orientation or velocity. In particular, we consider localization scenarios with
various numbers of RISs, single- or multi-antenna base stations, narrowband or
wideband transmissions, and near- and farfield operation. Furthermore, we
provide a short description of the general RIS operation together with radio
localization fundamentals, experimental validation of a localization scheme
with two RISs, as well as key research directions and open challenges specific
to RIS-enabled localization and sensing.
