  We summarize the state of the art and future directions in using millisecond
radio pulsars to test gravitation and measure intrinsic, fundamental parameters
of the pulsar systems. As discussed below, such measurements continue to yield
high-impact constraints on viable nuclear processes that govern the
theoretically-elusive interior of neutron stars, and place the most stringent
limits on the validity of general relativity in extreme environments. Ongoing
and planned pulsar-timing measurements provide the greatest opportunities for
measurements of compact-object masses and new general-relativistic variations
in orbits.
