This book is intended for an introductory course in digital logic design, which is a basic course in most electrical and computer engineering programs. A successful designer of digital logic circuits needs a good understanding of the classical methods of logic design and a firm grasp of the modern design approach that relies on computer-aided design (CAD) tools. The main goals of this book are (1) to teach students the fundamental concepts of classical manual digital design and (2) illustrate clearly the way in which digital circuits are designed today, using CAD tools. Even though current modern designers very rarely use manual techniques, our motivation for teaching such techniques is to give students an intuitive feeling for how digital circuits operate. The manual techniques also provide an illustration of the types of manipulations performed by CAD tools, giving students an appreciation of the benefits provided by design automation. Throughout the book, basic concepts are introduced by way of simple design examples, which we perform using both manual techniques and modern CAD-tool-based methods. After basic concepts are established, more complex examples are provided using the CAD tools. Thus, to illustrate how digital design is presently carried out in practice, our emphasis is on modern design methodology.