Modernization theory is used to explain the process of modernization within societies. The "classical" theories of modernization of the 1950s and 1960s drew on sociological analyses of Karl Marx, Emile Durkheim and a partial reading of Max Weber, and were strongly influenced by the writings of Harvard sociologist Talcott Parsons. Modernization theory was a dominant paradigm in the social sciences in the 1950s and 1960s, then went into a deep eclipse. It made a comeback after 1991, when Francis Fukuyama wrote about the end of the Cold War as confirmation on modernization theory and more generally of universal history. But the theory remains a controversial model.

Modernization refers to a model of a progressive transition from a "pre-modern" or "traditional" to a "modern" society. Modernization theory suggests that traditional societies will develop as they adopt more modern practices. Proponents of modernization theory claim that modern states are wealthier and more powerful and that their citizens are freer to enjoy a higher standard of living. Developments such as new data technology and the need to update traditional methods in transport, communication and production make modernization necessary or at least preferable to the status quo. That view makes critique difficult since it implies that such developments control the limits of human interaction, not vice versa. And yet, seemingly paradoxically, it also implies that human agency controls the speed and severity of modernization. Supposedly, instead of being dominated by tradition, societies undergoing the process of modernization typically arrive at forms of governance dictated by abstract principles. Traditional religious beliefs and cultural traits, according to the theory, usually become less important as modernization takes hold.

The theory looks at the internal factors of a country while assuming that with assistance, "traditional" countries can be brought to development in the same manner more developed countries have been. Modernization theory both attempts to identify the social variables that contribute to social progress and development of societies and seeks to explain the process of social evolution. Authors such as Daniel Lerner explicitly equated modernization with Westernization.

Today, the concept of modernization is understood in three different meanings: 1) as the internal development of Western Europe and North America relating to the European New Era; 2) as a process by which countries that do not belong to the first group of countries, aim to catch up with them; 3) as processes of evolutionary development of the most modernized societies (Western Europe and North America), i.e. modernization as a permanent process, carried out through reform and innovation, which today means a transition to a postindustrial society. Historians link modernization to the processes of urbanization and industrialization and the spread of education. As Kendall (2007) notes, "Urbanization accompanied modernization and the rapid process of industrialization." In sociological critical theory, modernization is linked to an overarching process of rationalisation. When modernization increases within a society, the individual becomes increasingly important, eventually replacing the family or community as the fundamental unit of society. It is also a subject taught in traditional Advanced Placement World History classes.

Modernization theory is subject to criticism originating among socialist and free-market ideologies, world-systems theorists, globalization theorists and dependency theorists among others. Modernization theory stresses not only the process of change but also the responses to that change. It also looks at internal dynamics while referring to social and cultural structures and the adaptation of new technologies.