This book examines constants, the role they play in the laws of physics, and whether indeed constants can be verified. From the laboratory to the depths of space, it explores the paths of gravitation, general relativity and new theories such as that of superstrings. Coverage investigates the solidity of the foundations of physics and discusses the implications of the discovery of the non-constancy of a constant. The book even goes beyond the subject of constants to explain and discuss many ideas in physics, encountering along the way, for example, such exciting details as the discovery of a natural nuclear reactor at Oklo in Gabon.