There remains, despite centuries of debate, no consensus about what makes humans intellectually and culturally different from other species, and even less so concerning the underlying sources of these differences. The main hypothesis of the project Stages in the Evolution and Development of Sign Use (SEDSU) is that it is not language per se, but an advanced ability to engage in sign use that constitutes the characteristic feature of human beings; in particular the ability to differentiate between the sign itself, be it gesture, picture, word or abstract symbol, and what it represents, i.e. the “semiotic function” (Piaget 1945). The project is highly interdisciplinary and the single research effort will afford new possibilities for methodological innovation, and the collection and analysis of new types of comparative data. The central research objective of the project is to investigate the developmental and comparative distribution of semiotic processes, and their effect on cognition. For this purpose we single out five cognitive domains, and propose to study their interrelations and role in the development of sign use. They are: (a) perception and categorisation, (b) iconicity and pictures, (c) spatial conceptualisation and metaphor, (d) imitation and mimesis and (e) intersubjectivity and conventions. They are all characterised by stage-like developmental profiles which we expect to correlate with differences in sign use. The investigations in the different domains will be carried out in parallel, with extensive sharing of methodologies and results. Since we hold that each domain plays a key role in providing cognitive prerequisites for the development of sign use, and at the same time is transformed by the acquisition of the latter, we expect to find considerable similarities and interactions between developments in the domains. Finally, we intend to integrate all the results of the SEDSU project in a coherent theory of semiotic development.