  We overview the history of primordial black hole (PBH) research from the
first papers around 50 years ago to the present epoch. The history may be
divided into four periods, the dividing lines being marked by three key
developments: inflation on the theoretical front and the detection of
microlensing events by the MACHO project and gravitational waves by the
LIGO/Virgo/KAGRA project on the observation front. However, they are also
characterised by somewhat different focuses of research. The period 1967-1980
covered the groundbreaking work on PBH formation and evaporation. The period
1980-1996 mainly focussed on their formation, while the period 1996-2016
consolidated the work on formation but also collated the constraints on the PBH
abundance. In the period 2016-2024 there was a shift of emphasis to the search
for evidence for PBHs and - while opinions about the strength of the purported
evidence vary - this has motivated more careful studies of some aspects of the
subject. Certainly the soaring number of papers on PBHs in this last period
indicates a growing interest in the topic.
