Bringing together some of the top researchers gravitational physics, the 1990 Banff Summer Institute on Gravitation focussed on three of the most exciting areas of research in this subject today: Cosmology, Quantum Gravity and Tests of Gravitational Theory. Besides covering the most up-to-date developments, special emphasis was placed upon the interdisciplinary aspects of each of these topics. The pedagogical character of the lectures is designed to bring graduate students up to the forefront of research.