Environmental history is the study of human interaction with the natural world over time, emphasising the active role nature plays in influencing human affairs and vice versa.

Environmental history first emerged in the United States out of the environmental movement of the 1960s and 1970s, and much of its impetus still stems from present-day global environmental concerns. The field was founded on conservation issues but has broadened in scope to include more general social and scientific history and may deal with cities, population or sustainable development. As all history occurs in the natural world, environmental history tends to focus on particular time-scales, geographic regions, or key themes. It is also a strongly multidisciplinary subject that draws widely on both the humanities and natural science.

The subject matter of environmental history can be divided into three main components. The first, nature itself and its change over time, includes the physical impact of humans on the Earth's land, water, atmosphere and biosphere. The second category, how humans use nature, includes the environmental consequences of increasing population, more effective technology and changing patterns of production and consumption. Other key themes are the transition from nomadic hunter-gatherer communities to settled agriculture in the Neolithic Revolution, the effects of colonial expansion and settlements, and the environmental and human consequences of the Industrial and technological revolutions. Finally, environmental historians study how people think about nature – the way attitudes, beliefs and values influence interaction with nature, especially in the form of myths, religion and science.

In 1967, Roderick Nash published Wilderness and the American Mind, a work that has become a classic text of early environmental history. In an address to the Organization of American Historians in 1969 (published in 1970) Nash used the expression "environmental history", although 1972 is generally taken as the date when the term was first coined. The 1959 book by Samuel P. Hays, Conservation and the Gospel of Efficiency: The Progressive Conservation Movement, 1890–1920, while being a major contribution to American political history, is now also regarded as a founding document in the field of environmental history. Hays is professor emeritus of History at the University of Pittsburgh. Alfred W. Crosby's book The Columbian Exchange (1972) is another key early work of environmental history.

Brief overviews of the historiography of environmental history have been published by J. R. McNeill, Richard White, and J. Donald Hughes. In 2014 Oxford University Press published a volume of 25 essays in The Oxford Handbook of Environmental History.

There is no universally accepted definition of environmental history. In general terms it is a history that tries to explain why our environment is like it is and how humanity has influenced its current condition, as well as commenting on the problems and opportunities of tomorrow. Donald Worster's widely quoted 1988 definition states that environmental history is the "interaction between human cultures and the environment in the past".

In 2001, J. Donald Hughes defined the subject as the "study of human relationships through time with the natural communities of which they are a part in order to explain the processes of change that affect that relationship". and, in 2006, as "history that seeks understanding of human beings as they have lived, worked and thought in relationship to the rest of nature through the changes brought by time". "As a method, environmental history is the use of ecological analysis as a means of understanding human history...an account of changes in human societies as they relate to changes in the natural environment". Environmental historians are also interested in "what people think about nature, and how they have expressed those ideas in folk religions, popular culture, literature and art". In 2003, J. R. McNeill defined it as "the history of the mutual relations between humankind and the rest of nature".

Traditional historical analysis has over time extended its range of study from the activities and influence of a few significant people to a much broader social, political, economic, and cultural analysis. Environmental history further broadens the subject matter of conventional history. In 1988, Donald Worster stated that environmental history "attempts to make history more inclusive in its narratives" by examining the "role and place of nature in human life", and in 1993, that "Environmental history explores the ways in which the biophysical world has influenced the course of human history and the ways in which people have thought about and tried to transform their surroundings". The interdependency of human and environmental factors in the creation of landscapes is expressed through the notion of the cultural landscape. Worster also questioned the scope of the discipline, asking: "We study humans and nature; therefore can anything human or natural be outside our enquiry?"