  Astrophysical transients have been observed for millennia and have shaped our
most basic assumptions about the Universe. In the last century, systematic
searches have grown from detecting handfuls of transients per year to over 7000
in 2018 alone. As these searches have matured, we have discovered both large
samples of "normal" classes and new, rare classes. Recently, a transient was
the first object observed in both gravitational waves and light. Ground-based
observatories, including LSST, will discover thousands of transients in the
optical, but these facilities will not provide the high-fidelity near-infrared
(NIR) photometry and high-resolution imaging of a space-based observatory.
WFIRST can fill this gap. With its survey designed to measure the expansion
history of the Universe with Type Ia supernovae, WFIRST will also discover and
monitor thousands of other transients in the NIR, revealing the physics for
these high-energy events. Small-scale GO programs, either as a supplement to
the planned survey or as specific target-of-opportunity observations, would
significantly expand the scope of transient science that can be studied with
WFIRST.
