This volume contains a number of essays by experts in areas of theoretical physics and astrophysics including cosmology, classical and quantum gravity, string theory and relativistic astrophysics. It provides reviews of current research in these frontier areas in the year 2000. Several of the essays emphasize alternative views of the Universe by leading astronomers and physicists who are known for their pioneering contributions. The volume is dedicated to Professor Jayant Narlikar, who has concerned himself with fundamental issues in cosmology and gravitation theory over a long and distinguished research career.