  Strong gravitational lensing and microlensing of supernovae (SNe) are
emerging as a new probe of cosmology and astrophysics in recent years. We
provide an overview of this nascent research field, starting with a summary of
the first discoveries of strongly lensed SNe. We describe the use of the time
delays between multiple SN images as a way to measure cosmological distances
and thus constrain cosmological parameters, particularly the Hubble constant,
whose value is currently under heated debates. New methods for measuring the
time delays in lensed SNe have been developed, and the sample of lensed SNe
from the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST) is
expected to provide competitive cosmological constraints. Lensed SNe are also
powerful astrophysical probes. We review the usage of lensed SNe to constrain
SN progenitors, acquire high-z SN spectra through lensing magnifications, infer
SN sizes via microlensing, and measure properties of dust in galaxies. The
current challenge in the field is the rarity and difficulty in finding lensed
SNe. We describe various methods and ongoing efforts to find these spectacular
explosions, forecast the properties of the expected sample of lensed SNe from
upcoming surveys particularly the LSST, and summarize the observational
follow-up requirements to enable the various scientific studies. We anticipate
the upcoming years to be exciting with a boom in lensed SN discoveries.
