X-ray crystallography provides us with the most accurate picture we can get of atomic and molecular structures in crystals. It provides a hard bedrock of structural results in chemistry and in mineralogy. In biology, where the structures are not fully crystalline, it can still provide valuable results and, indeed, the impact here has been revolutionary. It is still an immense field for young workers, and no doubt will provide yet more striking developments of a major character. It does, however, require a wide range of intellectual application, and a considerable ability in many fields. This book will provide much help. It is a very straightforward and thorough guide to every aspect of the subject. The authors are ex­ perienced both as research workers and as teachers of standing, and this is shown in their clarity of exposition. There are plenty of illustrations and worked examples to aid the student to obtain a real grasp of the subject. The practical side is encouraged by the very clarity of the theory.