Primordial black holes are black holes that may have formed in the early Universe. Their masses potentially span a range from as low as the Planck mass up to many orders of magnitude above the solar mass. This, in particular, includes black holes of the order of 10 solar masses, like those recently discovered by LIGO. These may be of primordial origin. In order to qualitatively and quantitatively asses this and related scenarios, a profound understanding of the holes’ formation mechanism necessary. After a general introduction on primordial black holes, I will discuss the most consequential aspects of their formation, and elaborate on the observable imprints these may leave. I will give an overview about recent abundance limits, and comment on constraints of combined scenarios in which also particle dark matter is present.