This chapter introduces Cas Mudde's minimal definition of populism as thin-centred ideology in which pure people and the elite are confronted and people's will promoted. It discusses this definition favoured by the so-called ideational populism approach in regard to key elements in various populism definitions, such as political ideologies, style and movements. In addition, Ernesto Laclau's understanding of populism as political identity formation through strong antagonist identifications of us and them is examined. Finally, the chapter outlines the cultural approach to populism that combines ideational and Laclaudian traditions and defines populism as a political identification process in which ideological and moral symbols and cultural markers are used to construct political agency of the people as opposite to their enemies.