  Light-pulse atom interferometers are highly sensitive to inertial and
gravitational effects. As such they are promising candidates for tests of
gravitational physics. In this article the state-of-the-art and proposals for
fundamental tests of gravity are reviewed. They include the measurement of the
gravitational constant $G$, tests of the weak equivalence principle, direct
searches of dark energy and gravitational-wave detection. Particular emphasis
is put on long-time interferometry in microgravity environments accompanied by
an enormous increase of sensitivity. In addition, advantages as well as
disadvantages of Bose-Einstein condensates as atom sources are discussed.
