Molecular biology proceeds at unremitting pace to unfold new secrets of the living world. Biology, long regarded as an inexact companion to physics and chemistry, has undergone transformation. Now, chemical and physical principles are tools in understanding highly complex biomolecular processes, whose origin lies in a history of chance, constraint and natural selection. The accuracy of these processes, often remarkably high, is crucial to their self­ perpetuation, both individually and collectively, as ingredients of the organism as a whole. In this book are presented thirteen chapters which deal with various facets of the accuracy problem. Subjects covered include: the specificity of enzymes; the fidelity of synthesis of proteins; the replication and repair of DNA: general schemes for the enhancement of biological accuracy; selection for an optimal balance between the costs and benefits of accuracy; and the possible relevance of molecular mistakes to the process of ageing. The viewpoints are distinct, yet complementary, and the book as a whole offers to researchers and students the first comprehensive account of this growing field.