The Northern League has played a fundamental role in the transformation of the Italian political system. The action of the new party had effects on different levels. First and foremost the Northern League contributed decisively to the crisis of the government parties in the years from 1989 to 1993, undermining their electoral consensus in the regions of Northern Italy. The Northern League deeply transformed the language, themes, issues and alliances which had characterized Italian political life in the previous thirty years. So the new party made a decisive contribution to the change in Italian political culture, which marked the birth of the so-called "Second Republic". In very few years the Northern League has succeeded in becoming the largest party in the regions of Northern Italy. The new party has gradually built an organisation with a capillary network of branches throughout the area, and a system of support organizations. In the process it has radically changed politics in Northern Italy by acting as a third pole ready to exploit every opportunity to feed popular protest. This essay analyzes both the fundamental characteristics of the new political subject and the ways the League's political initiatives have influenced changes in the Italian political system.