  The LIGO/Virgo detections of binary black hole mergers marked a watershed
moment in astronomy, ushering in the era of precision tests of Kerr dynamics.
We review theoretical and experimental challenges that must be overcome to
carry out black hole spectroscopy with present and future gravitational wave
detectors. Among other topics, we discuss quasinormal mode excitation in binary
mergers, astrophysical event rates, tests of black hole dynamics in modified
theories of gravity, parameterized "post-Kerr" ringdown tests, exotic compact
objects, and proposed data analysis methods to improve spectroscopic tests of
Kerr dynamics by stacking multiple events.
