This book covers the material from the first part of a lecture on information theory offered to students in their 6th semester at the Technical University of Braunschweig. It assumes basic knowledge in electrical engineering and communication technology. Starting from the model of a message transmission, the book discusses the message source, signal representation, and modulation. Since the message is a stochastic process, the necessary knowledge and methods of statistics are presented, along with the introduction of fundamental concepts of information theory. The transformations of the signal from the time domain to the frequency domain, which are important for signal representation, are only briefly explained, so some prior knowledge is required. Sampling, particularly Shannon's sampling theorem, is treated in detail.