The internet is an extraordinary knowledge infrastructure and the first with a global range, a generator of a radically new phenomenon: a metaculture based on hypertext. Its emergence is changing human interactions and social movements. The Open Access movement is the first and most important of these new movements in the network society: it works towards unrestricted access to the flow of signs and cultural products, challenges the appropriation methods of private commerce, rejects the reduction of knowledge to a product and demands the construction of a new public domain for developing a free culture by means of open access. This book introduces the characteristics of the different branches and their focus on the defence of a free culture and a rebuilding of the public sphere in a state of mobile communication.