Modernization theories represent one of the most important and most controversial approaches in transformation research. After their golden age in the 1950s and 1960s, they came under pressure by alternative approaches like World-Systems Analysis or actor-centred transition approaches. But modernization theories have experienced a renaissance with the epochal threshold of 1989/90 and the subsequent wave of democratization. Today, three major currents can be identified: neo-evolutionist approaches, structuralist modernization theory, and the approach of multiple modernities or comparative historical sociology. They consider transformation as a specific type of accelerated transition of traditional, partly, or alternatively modernized societies to hegemonic social modernity. Although all approaches have elaborated an explanatory interpretation framework for empirical analysis often combining various social levels, dimensions, and factors (like structures and actors, or economic and cultural factors), there is considerable need for further research and self-reflection concerning normative foundations, causal mechanisms, and their empirical operationalization, as well as ‘postmodern’ challenges.