Uneven and combined development (also known as "unequal and combined development", and similar to "uneven development") is a concept in Marxian political economy, Marxist sociology, political science and social geography. It refers to the different patterns of development within and between countries trading in the world economy, characterized by the coexistence of traditional and modern economic systems, as well as the coexistence of old and new political systems.

The idea was most famously used by Leon Trotsky in the early 20th century to analyze the possibilities for industrialization and political emancipation in the Russian Empire, and the likely future of the Tsarist regime. After 1905, the theory of uneven and combined development became the basis of the Trotsky's political perspective of permanent revolution. Trotsky rejected the idea that human society inevitably had to develop through a uni-linear sequence of necessary "stages" of modernization; instead, backward countries could adopt the most advanced knowledge and technology from other countries for the purpose of accelerated development, without the need to repeat all the preceding stages to get there.

In the 1990s and the early 21st century, the concept of uneven and combined development experienced an academic revival among Marxist scholars in fields such as development theory and economic geography. David Harvey endorsed the usefulness of this concept to understand the spatial development of global capitalism.

Trotsky's concept was originally inspired by a series of articles by Alexander Helphand (better known as "Parvus") on "War and Revolution" in the Russian journal Iskra in 1904. The theory was not exactly new; Nikolay Chernyshevsky, Vasily Vorontsov, and others had proposed similar ideas.

At first, Trotsky used this concept only to describe a characteristic evolutionary pattern in the worldwide expansion of the capitalist mode of production from the 16th century onwards, through the growth of a world economy which connected more and more peoples and territories together through trade, migration and investment. His focus was also initially mainly on the history of the Russian empire, where the most advanced technological and scientific developments co-existed with extremely primitive and superstitious cultures.

In the 1920s and 1930s, Trotsky increasingly generalised the concept of uneven and combined development to the whole of human history, and even to processes of evolutionary biology, as well as the formation of the human personality - as a general dialectical category.

The concept played a certain role in the fierce theoretical debates during the political conflict between the supporters of Joseph Stalin and Trotsky's Left Opposition, a debate which ranged from the historical interpretation of the Russian revolution and economic strategies for the transition to socialism, to the correct understanding of principles of Marxism.

Different countries, Trotsky observed, developed and advanced to a large extent independently from each other, in ways which were quantitatively unequal (e.g. the local rate and scope of economic growth and population growth) and qualitatively different (e.g. nationally specific cultures and geographical features). In other words, countries had their own specific national history with national peculiarities.