This dynamic textbook provides students with a concise and accessible introduction to the fundamentals of modern digital communications systems. Building from first principles, its comprehensive approach equips students with all of the mathematical tools, theoretical knowledge, and practical understanding they need to excel. It equips students with a strong mathematical foundation spanning signals and systems, probability, random variables, and random processes, and introduces students to key concepts in digital information sources, analog-to-digital conversion, digital modulation, power spectra, multi-carrier modulation, and channel coding. It includes over 85 illustrative examples, and more than 270 theoretical and computational end-of-chapter problems, allowing students to connect theory to practice, and is accompanied by downloadable Matlab code, and a digital solutions manual for instructors. Suitable for a single-semester course, this succinct textbook is an ideal introduction to the field of digital communications for senior undergraduate students in electrical engineering.