  A warm/hot dust component (at temperature $>$ 300K) has been detected around
$\sim$ 20% of stars. This component is called "exozodiacal dust" as it presents
similarities with the zodiacal dust detected in our Solar System, even though
its physical properties and spatial distribution can be significantly
different. Understanding the origin and evolution of this dust is of crucial
importance, not only because its presence could hamper future detections of
Earth-like planets in their habitable zones, but also because it can provide
invaluable information about the inner regions of planetary systems. In this
review, we present a detailed overview of the observational techniques used in
the detection and characterisation of exozodiacal dust clouds ("exozodis") and
the results they have yielded so far, in particular regarding the incidence
rate of exozodis as a function of crucial parameters such as stellar type and
age, or the presence of an outer cold debris disc. We also present the
important constraints that have been obtained, on dust size distribution and
spatial location, by using state-of-the-art radiation transfer models on some
of these systems. Finally, we investigate the crucial issue of how to explain
the presence of exozodiacal dust around so many stars (regardless of their
ages) despite the fact that such dust so close to its host star should
disappear rapidly due to the coupled effect of collisions and stellar radiation
pressure. Several potential mechanisms have been proposed to solve this paradox
and are reviewed in detail in this paper. The review finishes by presenting the
future of this growing field.
