The fundamental problem or core task of communication technology is to transmit a given flow of information with minimal energy and maximum speed over a disturbed channel with minimal probability of error. This chapter introduces this basic problem of communication—in short: the reliable and efficient transmission of information over disturbed channels. It explains how to design suitable methods for baseband transmission to reliably transmit information over disturbed channels. This includes the transmission over distortion-free channels that are disturbed by noise. Such channels are usually referred to as AWGN channels (Additive White Gaussian Noise). Initially, using the example of binary transmission, it is explained in detail how the useful signal and disturbance are evaluated on the transmission path by the individual components of the transmission system. Quality criteria are defined that are suitable for capturing the transmission quality. Essential influencing variables, dependencies, and resulting optimization options are identified and discussed. Subsequently, some of the insights gained are generalized and important criteria are derived that characterize high-performance transmission systems. Building on this, some improved and extended concepts are presented that enable the optimization of transmission systems and thus the improvement of the performance capability. Detailed numerical examples serve to illustrate the general insights gained and the principles developed.