  Einstein's general theory of relativity is the standard theory of gravity,
especially where the needs of astronomy, astrophysics, cosmology and
fundamental physics are concerned. As such, this theory is used for many
practical purposes involving spacecraft navigation, geodesy and time transfer.
Here I review the foundations of general relativity, discuss recent progress in
the tests of relativistic gravity, and present motivations for the new
generation of high-accuracy tests of new physics beyond general relativity.
Space-based experiments in fundamental physics are capable today to uniquely
address important questions related to the fundamental laws of nature. I
discuss the advances in our understanding of fundamental physics that are
anticipated in the near future and evaluate the discovery potential of a number
of the recently proposed space-based gravitational experiments.

General Relativity and Quantum Cosmology