It has now become commonplace to refer to the current period of capitalist development as the era of the ‘knowledge-based’ (OECD 1996) or ‘learning’ (Lundvall and Johnson 1994) economy. No matter which label one prefers, the production, acquisition, absorption, reproduction, and dissemination of knowledge is seen by many as the fundamental characteristic of contemporary competitive dynamics. Long before this parlance became popular, scholars had expressed a deep interest in distinguishing between different types of knowledge. Philosophers of knowledge such as Ryle (1949) and Michael Polanyi (1958; 1966) anticipated later developments in social constructivist thought by enunciating what was for them a crucial distinction between knowledge that could be effectively expressed using symbolic forms of representation—explicit or codified—and other forms of knowledge that defied such representation—tacit knowledge (see Reber 1995; Barbiero n.d.). Within the field of innovation studies and technological change, and especially since the publication of Nonaka and Takeuchi’s The Knowledge- Creating Company (1995), the distinction between tacit and codified knowledge has been accorded great significance. However, in characteristically prescient fashion Nelson and Winter (1982) in their classic work had already made extensive use of the concept, which informed their analysis of organizational routines within an evolutionary perspective on technological change. In drawing attention to this concept, these authors helped revive widespread interest in the earlier work of Michael Polanyi, to the point where tacit knowledge has come to be recognized as a central component of the learning economy, and a key to innovation and value creation. Moreover, tacit knowledge is also acknowledged as a prime determinant of the geography of innovative activity, since its central role in the process of learning through interacting tends to reinforce the local over the global. For a growing number of scholars, this explains the perpetuation and deepening of geographical concentration in a world of expanding markets, weakening borders, and ever cheaper and more pervasive communication technologies. Recently, tacit knowledge has received considerable attention within the field of industrial economics (see for e.g. Cowan, David, and Foray 2000; Johnson, Lorenz, and Lundvall 2002), where a process of critical re-examination has begun.