  The PREX experiment at Jefferson Laboratory measures the neutron radius of
208Pb with parity violating electron scattering in a way that is free from most
strong interaction uncertainties. The 208Pb radius has important implications
for neutron rich matter and the structure of neutron stars. We present first
PREX results, describe future plans, and discuss a follow on measurement of the
neutron radius of 48Ca. We review radio and X-ray observations of neutron star
masses and radii. These constrain the equation of state (pressure versus
density) of neutron rich matter. We present a new energy functional that is
simultaneously fit to both nuclear and neutron star properties. In this
approach, neutron star masses and radii constrain the energy of neutron matter.
This avoids having to rely on model dependent microscopic calculations of
neutron matter. The functional is then used to predict the location of the drip
lines and the properties of very neutron rich heavy nuclei.
