Phone: +44 (0)207 919 7871.Face-space: A unifying concept. 2 AbstractThe concept of a multi-dimensional psychological space, in which faces can be represented according to their perceived properties, is fundamental to the modern theorist in face processing. Yet the idea was not clearly expressed until 1991. The background that led to Valentine's (1991a) face-space is explained and its continuing influence on theories of face processing is discussed. Research that has explored the properties of the face-space and sought to understand caricature, including facial adaptation paradigms is reviewed. Facespace as a theoretical framework for understanding the effect of ethnicity and the development of face recognition is evaluated. Finally two applications of face-space in the forensic setting are discussed. From initially being presented as a model to explain distinctiveness, inversion and the effect of ethnicity, face-space has become a central pillar in many aspects of face processing. It is currently being developed to help us understand adaptation effects with faces. While being in principle a simple concept, face-space has shaped, and continues to shape, our understanding of face perception.