This book deals with the relationship between gravitation and elementary particle physics, and the implications of these subjects for astrophysics. There has, in recent years, been renewed interest in theories that connect up gravitation and particle physics, and in the astrophysical consequences of such theories. Some of these accounts involve a time-variation of the Newtonian gravitational parameter, G. In this respect, the present book may be regarded as a companion to my Cosmology and Geophysics (Hilger, Bristol, 1978). There is some overlap as regards the discussion of G-variability, but...