Overurbanization is a thesis originally developed by scholars of demography, geography, ecology, economics, political science, and sociology in thrergence of International Nongovernmental Organizations Amid Declining States. The term is intentionally comparative and has been used to differentiate between developed and developing countries. Several causes have been suggested, but the most common is rural-push and urban-pull factors in addition to population growth.

The concept of overurbanization first emerged in the mid-20th century to describe cities whose rate of industrialization was growing more slowly than their rate of urbanization. According to sociologist Josef Gugler, the concept was "widely accepted in the 1950s and into the 1960s" and was split into two approaches, a diachronic and a synchronic approach. The synchronic approach, the main one taken in the 1950s, was proposed by sociologists Kingsley Davis and Hilda Golden who defined whether a country was overurbanized based on how its relationship between industrialization and urbanization compared to that of other countries during the same time period. Specifically, countries considered part of the Third World were compared to countries deemed part of the First World. Davis and Golden used data on "the percentage of economically active males not engaged in agriculture and the percentage of the population in cities of 100,000 or above in a large number of the countries in the world," in order to define the normal relationship between industrialization and urbanization. They then determine that countries whose rate of urbanization is significantly higher than normal in relation to their rate of industrialization are "overurbanized." The authors calculate an "expected" level of urbanization based on the rates of urbanization of other countries of the world at similar levels of industrialization (measured by percentage of males not engaged in agriculture). A few countries in particular that Davis and Golden measured as having higher levels of urbanization than expected were Egypt, Greece, and South Korea. Davis and Golden did not see overurbanization as a necessarily negative phenomenon, but rather a statistical reality that could have its challenges but would ultimately be self-correcting as an appropriate balance was found between levels of urbanization and industrialization. Scholars on overurbanization agree that N.V. Sovani was one of the first to discount Davis and Golden's argument, as he found that the connection between urbanization and industrialization was more significant in underdeveloped countries than developed ones, suggesting that Davis and Golden's measure of a "normal" relationship between urbanization and industrialization was not valid.

The definition offered by the United Nations and UNESCO in 1956 took a different approach to measuring overurbanization: the diachronic approach. A 1956 UNESCO report measured overurbanization historically, emphasizing that "at comparable levels of urbanization developed countries of today had a correspondingly greater proportion of their labour force engaged in non-agricultural occupations" than underdeveloped countries. Authors on overurbanization give the examples of France, the United States, Germany, and Canada as developed and often mention the continents of Asia and Africa as well as the region of Latin America as underdeveloped. This historical approach was applied to Asia in the report, which argued that because a smaller percentage of the labor force was engaged in non-agricultural activities than certain Western developed countries had at similar levels of urbanization, Asia was overurbanized. However, this method has been criticized by scholars who argue that it supports an ethnocentric idea that all countries follow the same path of development. Furthermore, economist N.V. Sovani argued that the evidence offered is not consistent with the development trajectories of developed countries, pointing out specific examples of developed countries such as Switzerland where high levels of industrialization did not correspond with high levels of urbanization. Sociologists John D. Kasarda and Edward Crenshaw pointed out that it was not so much the rate of urbanization of developing countries that was greater, but the absolute numbers of people migrating.

Scholars reference N.V. Sovani as a researcher who questioned whether to accept the 1950s definition of overurbanization. His debunking of the formerly accepted definitions of overurbanization encouraged further scholarly analysis and attempts to redefine the term. Sovani suggested that claims of overurbanization in underdeveloped countries stemmed from the perception that rapid urbanization had negative consequences. However, he claimed that there still lacked evidence for the idea that rapid urbanization actually made areas worse off. Economist David R. Kamerschen found that there was little statistical evidence to support that "rapid urbanization in underdeveloped countries hampers economic growth," suggesting that the phenomenon of overurbanization is questionable.

Following Sovani's work, several scholars offered alternative definitions, many of which included not just the relationship between population growth and their means of employment but also the ability of the urban area to provide public services, reflecting that economic development lagged behind population growth in a multitude of ways. Several scholars also increasingly embraced a negative connotation for the term. Urban planner John Dyckman suggested that inability to accommodate the expectations of migrants to the city made overurbanization a threat to social order. Economists Philip Graves and Robert Sexton argue that the definition of overurbanization must "involve the presence of negative net external effects for the city size in question," suggesting that as long as "positive external social benefits" from rapid urbanization dominate negative externalities, overurbanization is not at play. Gugler defined overurbanization by two factors: that migration to cities led to a "less than optimal allocation of labor between the rural and urban sectors" and that migration to cities "increases the costs of providing for a country's growing population." Sociologist Glenn Firebaugh disagreed, arguing that if overurbanization is caused by overpopulation, that overpopulation of rural areas could be worse than overpopulation of urban areas.

From its origins, the term has been used to differentiate between countries that are considered developed and underdeveloped. Davis and Golden considered a country to be underdeveloped if over half its economically active males were employed in agriculture. The UNESCO report frequently used the terms "developed" and "Western" in conjunction. Gugler and others use the terms "third world" and "first world" in their discussion.

Sociologist John Shandra states that arguments about the causes of overurbanization fall into five groups:

Shandra's analysis of several variables related to each of these categories suggested that all of these arguments have significant evidence except for the economic modernization perspective. Recent scholars believe that a variety of these factors are relevant.