  Nuclear mass measurements and neutron matter theory tightly constrain the
nuclear symmetry energy parameters $J$, $L$, $K_{sym}$ and $Q_{sym}$.
Corroboration of these constraints on $J$ and $L$ can be found from
measurements of the neutron skin thicknesses and dipole polarizabilities of
neutron-rich nuclei. The experimental constraints on these parameters are
compared with those obtained from consideration of astrophysical measurements
of the neutron star radius, which we show is highly correlated with $L$.
Attention is aimed at the recent PREX and CREX neutron skin measurements from
Jefferson Lab, NICER neutron star radius measurements, and a new interpretation
of the GW170817 tidal deformability measurement. We find joint satisfaction of
PREX and CREX gives $J=32.2\pm1.7$ MeV and $L=52.9\pm13.2$ MeV, in excellent
agreement with neutron matter predictions of $J=32.0\pm1.1$ MeV and
$L=51.9\pm7.9$ MeV.
