  This Astro2010 science white paper provides an overview of the opportunities
in low-frequency gravitational-wave astronomy, a new field that is poised to
make significant advances. While discussing the broad context of
gravitational-wave astronomy, this paper concentrates on the low-frequency
region (10^(-5) to 1 Hz), a frequency range abundantly populated in strong
sources of gravitational waves including massive black hole mergers,
ultra-compact stellar-mass galactic binaries, and capture of compact objects by
massive black holes in the nuclei of galaxies.
