The best-known uses of pulsars for testing the predictions of
gravitational theories are those in which the predicted
strong-field effects are compared directly against observations.
As essentially point-like objects in strong gravitational fields,
neutron stars in binary systems provide extraordinarily clean
tests of these predictions. This section will cover the relation
between the ``post-Keplerian'' timing parameters and strong-field
effects, and then discuss the three binary systems that yield
complementary high-precision tests.