The notions of 'function', 'feature' and 'functional feature' are associated with relatively new developments and insights in several areas of cognition. This book brings together different definitions, insights and research related to defining these notions from such diverse areas as language, perception, categorization and development. Each of the contributors in this book explicitly defines the notion of 'function', 'feature' or 'functional feature' within their own theoretical framework, presents research in which such a notion plays a pivotal role, and discusses the contribution of functional features in relation to their insights in a particular area of cognition. As such, this book not only presents new developments devoted to defining 'function', 'feature' and 'functional feature' in several sub-disciplines of cognitive science, but also offers a focused account of how these notions operate within the cognitive interface linking language and spatial representation. All book chapters are accessible for the interested novice, and offer the specialized researcher new empirical and theoretical insights into defining function, both with respect to the language and space interface and across cognition. The introduction to the book presents the reader with the main issues and viewpoints that are discussed in more detail in each of the book chapters.