  With the direct discovery of gravitational waves, black holes have regain
interest in the recent years. In particular primordial black holes (PBHs),
which originate from the very early Universe, may constitute (at least in part)
dark matter. The possibility that dark matter is made of black holes is
particularly appealing, and multi-messenger searches are important to probe
this hypothesis. In this paper I will discuss the concept of primordial black
holes, their origins, their characteristics and the current constraints. In
addition I will explain that the study of black holes is of utmost interest
since they may constitute portals to new physics and to quantum gravity.
