This book, which is the result of a project of Research of Relevant National Interest (PRIN 2007), presents an overview of theoretical-political thought as a challenge to centralism, starting from the late Middle Ages and the Modern Age through to the twentieth century. As against a 'vertical' vision of European politics which, from Machiavelli to Mosca, favours the hierarchical nature of power relations, the essays collected here are presented as a number of brief chapters in the history of the 'horizontal paradigm' in European political thought. They demonstrate the wealth and the persistence of a tradition and of the myriad experiences and theorisations that have, in effect, proposed forms of decentralisation and of association frequently coexisting with centralism, as in the case of the autonomies within the system of the great national states.