Spoken language is a rapidly unfolding signal: a complex code that the listener must crack to understand what is being said. From the structures of the inner ear through to higher-order areas of the brain, a hierarchy of interlinked processes transforms the acoustic signal into a linguistic message within fractions of a second. This Element outlines how we perceive speech and explores what the auditory system needs to achieve to make this possible. It traces a path through the system and discusses the mechanisms that enable us to perceive speech as a coherent sequence of words. This is combined with a brief history of research into language and the brain beginning in the nineteenth century, as well as an overview of the state-of-the-art neuroimaging and analysis techniques that are used to investigate phonetics in the brain today. This title is also available as Open Access on Cambridge Core.