  The structure of neutron stars is considered from theoretical and
observational perspectives. We demonstrate an important aspect of neutron star
structure: the neutron star radius is primarily determined by the behavior of
the pressure of matter in the vicinity of nuclear matter equilibrium density.
In the event that extreme softening does not occur at these densities, the
radius is virtually independent of the mass and is determined by the magnitude
of the pressure. For equations of state with extreme softening, or those that
are self-bound, the radius is more sensitive to the mass. Our results show that
in the absence of extreme softening, a measurement of the radius of a neutron
star more accurate than about 1 km will usefully constrain the equation of
state. We also show that the pressure near nuclear matter density is primarily
a function of the density dependence of the nuclear symmetry energy, while the
nuclear incompressibility and skewness parameters play secondary roles.
  In addition, we show that the moment of inertia and the binding energy of
neutron stars, for a large class of equations of state, are nearly universal
functions of the star's compactness. These features can be understood by
considering two analytic, yet realistic, solutions of Einstein's equations,
due, respectively, to Buchdahl and Tolman. We deduce useful approximations for
the fraction of the moment of inertia residing in the crust, which is a
function of the stellar compactness and, in addition, the presssure at the
core-crust interface.
