One of the exciting aspects of being involved in the field of molecular biology is the ever accelerating rate of progress, both in the development of new methodologies and the practical applications of these methodol - ogies. Indeed, such developments led to the idea of the first edition of Molecular Biology and Biotechnology and subsequent editions have reflected the fast moving nature of the area. To keep pace with the ever expanding technological changes we have increased the basic molecular biology content of the book from one to two chapters in this latest edition. In recent years the development of the World Wide Web has been exponential and now provides an essential source of information and access to databases for the molecular biologist. We therefore considered it both appropriate and timely to include a new chapter devoted to the subject of Bioinformatics. Other chapter titles remain the same as the previous edition but this should not mask the significant updating of the content of these chapters in response to major develop - ments in each area. Indeed, in order to reflect research developments, the majority of these chapters have required a total re-write rather than simple updating.