  Solar flares are due to the catastrophic release of magnetic energy in the
Sun's corona, resulting in plasma heating, mass motions, particle acceleration,
and radiation emitted from radio to $\gamma$-ray wavelengths. They are
associated with global coronal eruptions of plasma into the interplanetary
medium---coronal mass ejections---that can result in a variety of "space
weather" phenomena. Flares release energy over a vast range of energies, from
$\sim\!10^{23}$ ergs (nanoflares) to more than $10^{32}$ ergs. Solar flares are
a phenomenon of general astrophysical interest, allowing detailed study of
magnetic energy release, eruptive processes, shock formation and propagation,
particle acceleration and transport, and radiative processes. Observations at
radio wavelengths offer unique diagnostics of the physics of flares. To fully
exploit these diagnostics requires the means of performing time-resolved
imaging spectropolarimetry. Recent observations with the Jansky Very Large
Array (JVLA) and the Expanded Owens Valley Solar Array (EOVSA), supported by
extensive development in forward modeling, have demonstrated the power of the
approach. The ngVLA has the potential to bring our understanding of flare
processes to a new level through its combination of high spatial resolution,
broad frequency range, and imaging dynamic range---especially when used in
concert with multi-wavelength observations and data at hard X-ray energies.
