The objective of this book is to provide an introduction to the basic principles in analog and digital communications for advanced undergraduates and post graduates in electrical or computer engineering. The assumed background is circuit analysis, and prior exposure to signals and systems course is helpful. The book can be used as a self-contained textbook or for self-study. Each topic is discussed in detail. Major purposes of the book are to add organization and structure to a field that has grown and continues to grow rapidly, and to ensure awareness of the “big picture” even while delving into the details. Signals and key processing steps are traced from the information source through the transmitter, channel, receiver, and ultimately to the information sink. Throughout the book, emphasis is placed on system goals and the need to trade off basic system parameters such as signal-to-noise ratio, probability of error, and bandwidth expenditure.