Any signal must get from a sender to a receiver if information is to be transmitted. In the case of bird song, the acoustic properties of the habitat may hinder this being achieved. However, birds as senders and receivers have evolved numerous adaptations to overcome the problem of getting the message across. In this chapter, we explore habitat-dependent patterns of sound transmission, the effects of noise, signal perception, and signal interpretation such as auditory distance assessment with a specific focus on the solutions that selection has generated. We argue that along with other possible selective forces, such as sexual selection, the combination of environmental constraints on signal transmission, noise levels, and the use of signal degradation as a distance cue need mutual consideration to gain a more thorough understanding of the astounding variety of avian song and the many different ways in which birds use it.