The idea that geographical proximity is essential, and even sometimes, consubstantial with the transfer of knowledge and innovations, is widely accepted, by decision makers and innovation specialists alike. It was the dogma of the 1980s and 90s; one that has been fostered by the success of some local systems such as the mythical Silicon Valley and Route 128, or closer to home, Sophia Antipolis. The saga of clusters is at the origin of theoretical objects that have now become development tools used by great international institutions such as the OECD or the World Bank.

Many studies have focused on these approaches, and more particularly on geographic spillovers, local innovation systems approaches or knowledge economics. But these analyses are all based on one idea: the co-location of innovative firms and possibly of private or public research laboratories is a favourable precondition to the development of innovation activities. Herein lies the interest of the spatial concentration of innovation; concentration which must facilitate the diffusion of ideas, knowledge and information at local level; while informal meetings and local partnerships contribute positively to the development of technologically innovative projects.

However, serious doubts are emerging about the validity and legitimacy of this hypothesis. In addition to the empirical finding that it is impossible to build everywhere and successfully local innovation systems, we now find that this type of approach has severe limitations (Rallet & Torre, 2006, introduction; Massard & Torre, 2004). My research work lies within the framework of a re-examination of the role played by space in the coordination of actors and an evaluation of that of the co-existence of geographical proximity and organized proximity. My work sheds some light on three questions in particular.

Mes recherches apportent des éclairages sur trois points particuliers.

• The constraint of geographical proximity is relative

Although the constraint of geographical proximity still holds in certain types of production and transaction activities, its role in economic coordination is not absolute, particularly in knowledge and information intensive activities (Rallet & Torre, 2001). The geographical concentration of individuals and organizations and the demonstrated existence of (partly) local innovation and production systems can be explained by the embedding of economic relations within social networks with strong territorial ties, and by the interaction between local institutions that actively promote innovation. Furthermore, the organizational and institutional dimensions are determinant (Filippi & Torre, 2003) and the success or competitiveness of certain localized systems can often be explained by the existence of organized proximity relationships. A technology park, a science park or a competitive cluster exists above all thanks to the work of an organizational structure that attracts firms or laboratories, brings the main protagonists together, instils them with a sense of local belonging and promotes the image of the innovation system. What is more, the role played by the local institutions – or by the decentralized State departments – is also central to the success of localized innovation systems.

• The ambiguity of the notion of cluster

We show that the success of the notion of cluster rests on a naturalist hypothesis according to which the tacit dimension of the knowledge exchanged between the actors of the production and innovation systems necessitates face to face relations and therefore the co-location of these actors within the same geographical areas; in short it necessitates the development of localized innovation systems. But this hypothesis is easily invalidated because it rests on incoherent foundations, particularly with respect to the public and tacit nature of knowledge (Torre, 2008). Re-examining clusters from a perspective of proximity reveals that analysing them as places where both types of proximity (geographical and organized) are combined is more legitimate and that it is the mobilisation of organized proximity – and its associated logics of belonging and similarity - by firms or institutions that is central (Torre, 2006). Networks, common projects, public action are at the heart of these processes. The geographical proximity of the actors of knowledge cannot alone ensure the success of clusters; The processes of spatial agglomerations of research and innovative activities can often be explained by traditional economic factors such as the attractiveness of an area due to land prices, tax and financial advantages or the benefits of being located in proximity of a pool of qualified labour.

• The essential role of Temporary Geographical Proximity

A dose of geographical proximity is undeniably essential to the development and success of joint projects undertaken by different firms or organizations. But meeting this need does not necessarily require the permanent co-location of research, innovation or production activities. En effet, la nécessité de proximité géographique affecte surtout, aujourd’hui, Indeed, geographical proximity is nowadays mostly necessary during the first stages of the processes of production, research and development. It is necessary for people to meet face to face, during the first stages of the collaboration, in order to develop mutual trust, to agree on and plan the future stages of the project. Subsequently, the relations of organized proximity thus established can then be maintained from a distance, particularly thanks to IT (Torre 2008). Temporary meetings, taking place at regular intervals at one of the partners' offices or in places dedicated to meetings, are then sufficient to exchange the information the partners need in order to cooperate and to solve possible conflicts (Rallet & Torre, 2009). The mobility of individuals implies a strong relation to space but one that differs in nature from that described by the traditional approaches. I call it Temporary Geographical Proximity and I shall now describe its characteristics.

Taking into account the combination of the different types of proximity helps to view the typologies of territories as well as the processes of creation and of transmission of knowledge. Organized proximity is always essential to the process of coordination between partners working together, but from a distance, on production, research or development projects. It facilitates interaction between human beings, whether it takes the form of exchanges between the latter, or of shared values or mental representations. But this organized proximity combines with different forms of spatial proximity relations, such as permanent geographical proximity, which leads to the co-location of partners - for example within localized systems of production or clusters – or temporary geographical proximity, which above all requires the physical mobility of the actors involved in a process of long distance cooperation so that they can meet face to face in heterotopic sites. Finally, ICT can compensate for the lack of co-presence but in most cases, it combines with and facilitates mobility (i.e. short or long business trips).