  The self-force describes the effect of a particle's own gravitational field
on its motion. While the motion is geodesic in the test-mass limit, it is
accelerated to first order in the particle's mass. In this contribution I
review the foundations of the self-force, and show how the motion of a small
black hole can be determined by matched asymptotic expansions of a perturbed
metric. I next consider the case of a point mass, and show that while the
retarded field is singular on the world line, it can be unambiguously
decomposed into a singular piece that exerts no force, and a smooth remainder
that is responsible for the acceleration. I also describe the recent efforts,
by a number of workers, to compute the self-force in the case of a small body
moving in the field of a much more massive black hole. The motivation for this
work is provided in part by the Laser Interferometer Space Antenna, which will
be sensitive to low-frequency gravitational waves. Among the sources for this
detector is the motion of small compact objects around massive (galactic) black
holes. To calculate the waves emitted by such systems requires a detailed
understanding of the motion, beyond the test-mass approximation.
