  Twenty-one years after Bohdan's seminal paper launched the field of
gravitational microlensing, it has radically diversified from a method narrowly
focused on finding dark matter to a very general astronomical tool.
Microlensing has now detected 12 planets, including several that are
inaccessible by other search methods. It has resolved the surfaces of distant
stars, served as a magnifying glass to take spectra of extremely faint objects,
and revealed a number of surprising phenomena. I take a sweeping look at this
remarkable technique, giving equal weight to its successes and to the tensions
that are continuing to propel it forward.
