Laughter is a non-verbal emotional expression: although we associated laughter with amusement, laughter has its roots in mammalian play vocalizations, and is associated with social interactions. In this talk I will explore the evolution of laughter, the ways that it is used by humans and other mammals, and some of the complexities of how our brains process laughter. I will argue that laughter is used by adult humans in a highly nuanced way, and that scientists should be paying more attention to laughter.