  We summarize the current status on constraining the density dependence of the
symmetry energy from terrestrial laboratory measurements and astrophysical
observations. While the value $E_{sym}({\rho_{0}})$ and density slope $L$ of
the symmetry energy at saturation density $\rho_{0}$ can vary largely depending
on the data or methods, all the existing constraints are essentially consistent
with $E_{sym}({\rho_{0}}) = 31 \pm 2$ MeV and $L = 50 \pm 20$ MeV. The
determination of the supra-saturation density behavior of the symmetry energy
remains a big challenge.
