Pulsars are radio-emitting neutron stars, and therefore offer the opportunity

to probe relativistic effects near strongly self-gravitating objects.

Pulsars orbiting white dwarfs, which are far less dense, allow for tests of 

various equivalence principles.  Pulsars in double-neutron-star binaries 

often permit the measurement of multiple relativistic corrections to a 

Keplerian orbit, resulting in self-consistency tests for different 

gravitational theories.  I will review the principles of pulsar timing and 

the current status of these various tests, including the latest results

from the only known double-pulsar system.  I will also discuss the 

prospects for direct detection of gravitational waves via pulsar timing.