In this newly revised edition of Digital Logic Design, we have taken the opportunity to undertake extensive revisions of much material contained in the third edition, whilst retaining its comprehensive coverage of the subject. Like the previous editions, the current edition is intended to cover all the material that is needed in a typical undergraduate or Master's course on Digital Logic Systems, and also to act as a reference text for graduates working in this field. To this end, we have retained all elementary material assuming little or no background, but the advanced chapters have accordingly been revised to take account of recent trends in hardware availability. A number of additional problems have been set at the end of some of the chapters, sometimes without answers, in order to allow the reader to exercise his/her design capabilities without the luxury of being able to refer to worked solutions. The chapter on instrumentation and interfacing is almost entirely new, and the chapters on programmable logic devices, and on fault diagnosis and testing, have been considerably enlarged as a result, on the one hand, of significant advances in the technology and the range of devices now available to the designer, and on the other hand to emphasise that logical fault-finding methods, far from being esoteric, impossible to apply in practice, trivial, or demeaning for a professional engineer to use, are actually worthy of serious study and application. Material enclosed in boxes in this manner is usually not needed later in this text, and is not as important as the main narrative, or sometimes summarises work in the main text. This material may be rather more demanding than the main text, or be unusual or obscure in some other manner; generally speaking, proofs of results in these sections and subsections are not given in detail, and are left as more of a challenge for the interested reader to work out in full. The first-time reader, or a reader not aiming for complete coverage of all the material in this text, may safely ignore these sections and subsections. Throughout the main part of this edition, we have used the 'old' IEEE logic symbols rather than the 'new' BS3939 symbols; this is a result of a perceived shift in attitudes in the engineering profession, and the IEEE symbols are now recommended alongside the BS symbols. Modern CAD systems are capable of printing the 'old' symbols with ease, eliminating the major initial advantage of the 'new' symbols when first introduced. However, as an understanding of the 'new' symbols is also a useful accomplishment, a summary of the 'new' system is included as an Appendix.