  The time domain of the sky has been only sparsely explored. Nevertheless,
recent discoveries from limited surveys and serendipitous discoveries indicate
that there is much to be found on timescales from nanoseconds to years and at
wavelengths from meters to millimeters. These observations have revealed
unexpected phenomena such as rotating radio transients and coherent pulses from
brown dwarfs. Additionally, archival studies have found not-yet identified
radio transients without optical or high-energy hosts. In addition to the known
classes of radio transients, possible other classes of objects include
extrapolations from known classes and exotica such as orphan gamma-ray burst
afterglows, radio supernovae, tidally-disrupted stars, flare stars, magnetars,
and transmissions from extraterrestrial civilizations.
  Over the next decade, meter- and centimeter-wave radio telescopes with
improved sensitivity, wider fields of view, and flexible digital signal
processing will be able to explore radio transient parameter space more
comprehensively and systematically.
