  Gravitational microlensing finds planets through their gravitational
influence on the light coming from a more distant background star. The presence
of the planet is then inferred from the tell-tale brightness variations of the
background star during the lensing event, even if no light is detectable from
the planet or the host foreground star. This review covers fundamental
theoretical concepts in microlensing, addresses how observations are performed
in practice, the~challenges of obtaining accurate measurements, and explains
how planets reveal themselves in the data. It~concludes with a presentation of
the most important findings to-date, a description of the method's strengths
and weaknesses, and a discussion of the future prospects of microlensing.
