It is the tradition of this series of workshops that theorists and experimentalists sharing common interests discuss a variety of issues relevant to promoting the quest to unify microscopic physics and gravitation. This proceedings volume embodies that tradition. The papers are taken from the Fourth International Workshop on Gravitation and Astrophysics. They cover topics such as superconducting accelerometers, low-temperature-long-distance telescopes for gravitational waves, gravitational experiment with high-precision torsion pendulums and modern high-technology, physics of neutron stars,...