This guide to modern biology was inspired by the explosion of new work in many areas of biology that has been fuelled by the application of recombinant DNA techniques. The fruits of recombinant DNA research also affects us in the applications to medicine, agriculture and industry and this is also covered. The book is designed to be a guide to certain key areas of biology, the framework of ideas in which new work is interpreted and the connections that are being made between hitherto separate areas of research. It is intended both as a quick reference source for individual topics and as a more general introductory reading for the student or non-specialist. Some general knowledge of biology, basic biochemistry and chemistry has had to be assumed in most sections. Each chapter starts with a general introduction, setting the subject in context. This is followed by a series of short sections on individual topics. These are arranged so that those unfamiliar with the subject area can work their way through from the beginning; the more knowledgeable reader can use the index to find individual sections of interest. Those sections of more general interest should be accessible to anyone with an interest in biology. The scope of the book has been deliberately restricted to areas of biology that can be directly addressed in terms of molecular genetics and cell structure and function, with a strong bias towards animal cells and mammalian and human biology. It therefore does not cover subjects such as ecology, animal behaviour and classical evolutionary biology, or psychology, which are concerned with a different level of biological organization. A selection of basic texts is given at the end of the book, along with guidance for the non-specialist on where to look for information. In addition, a list of further reading is provided at the end of each chapter.