  The nature of gravity is fundamental to our understanding of our own solar
system, the galaxy and the structure and evolution of the Universe. Einstein's
general theory of relativity is the standard model that is used for almost
ninety years to describe gravitational phenomena on these various scales. We
review the foundations of general relativity, discuss the recent progress in
the tests of relativistic gravity, and present motivations for high-accuracy
gravitational experiments in space. We also summarize the science objectives
and technology needs for the laboratory experiments in space with laboratory
being the entire solar system. We discuss the advances in our understanding of
fundamental physics anticipated in the near future and evaluate discovery
potential for the recently proposed gravitational experiments.
