When the first edition of this book was published in 1950, it predated the publication of the double-helical structure of DNA by three years. It is not, therefore, surprizing that nothing of the original book remains in the current edition. Indeed, such is the pace of change in the field of nucleic acids that less than 50% of material incorporated into the 1986 edition has been retained. The book aims at the advanced undergraduate and at graduates that are undertaking course work or requiring an in-depth background for their research. It also aims to provide the established scientist with a single text that permits updating across the whole field from DNA structure, replication and repair, through gene expression and its control to protein synthesis. Every chapter is accompanied by thorough referencing that enables the reader to evaluate personally the data and methodology that cannot be included in the text. In an attempt to keep this list within bounds, references are limited to about ten per page and, to accommodate the more recent literature, many of the older references have been left out in this latest edition.