What does it mean to know a language? Language is our primary tool for communication, and speaking, listening, reading, and writing are integral to our everyday lives. This chapter explores how adults use and understand language, from speech to the written word. We deconstruct the processes that are involved when speakers speak and listeners listen, and when readers read, and writers write. We delve into groundbreaking (and often controversial) studies to find out what they can tell us about speech production and comprehension. We’ll also find that a big part of language use is misuse. We look at the typical language of adults and the normal mistakes we make in our speech everyday, from mondegreens and malapropisms to spoonerisms and other slips of the tongue. We discuss what these speech and hearing errors mean, and what they reveal about the way language is organized in our minds.