Academic interest in the phenomenon of joint attention -- the capacity to attend to an object together with another creature -- has increased rapidly over the past two decades. Yet it isn't easy to spell out in detail what joint attention is, how it ought to be characterized, and what exactly its significance consists in. The writers for this volume address these and related questions by drawing on a variety of disciplines, including developmental and comparative psychology, philosophy of mind, and social neuroscience. The volume organizes their contributions along three main themes: definitional concerns, such as the question of whether or not joint attention should be understood as an irreducibly basic state of mind; processes and mechanisms obtaining on both the neural and behavioral levels; and the functional significance of joint attention, in particular the role it plays in comprehending spatial perspectives and understanding other minds. The collected papers present new work by leading researchers on one of the key issues in social cognition. They demonstrate that an adequate theory of joint attention is indispensable for a comprehensive account of mind.