Eco-nationalism (also known as ecological nationalism or green nationalism) is a synthesis of nationalism and green politics. Eco-nationalists may be from many points across the left–right political spectrum, but all are bound to the idea that the nation-state and its citizens have a special duty to protect the environment of their country.

According to Jane Dawson, eco-nationalism is the rise of social movements that closely connect problems of environment protection with nationalist concerns. Dawson also surmised that eco-nationalism is "the synthesis of environmentalism, national identity, and the struggle for justice". Professors of history K. Sivaramakrishnan and Gunnel Cederlöf have defined eco-nationalism as, whether nativist or cosmopolitan in nature, "when the state appropriates the environment and environmental policies as forms of national pride, thereby consolidating and legitimating the nation."

One of the first instances of eco-nationalism was in the 1980s in the then Soviet Union, where citizens perceived environmental degradation as both a systemic fault of socialism and a direct result of Moscow's desire to weaken a particular nation by destroying its natural base, and exploiting its resources. Estonian, Lithuanian and Ukrainian independence movements drew great strength from environmental activism, especially from an antinuclear stance. In 1985–1991, eco-nationalism was one of the symptoms and at the same time a new impulse of the disintegration of the Soviet Union.

Eco-nationalism as defined by anthropologists often manifests in the adoption of nature as an entity outside of culture that must be protected in its pristine and untouched state whenever possible. In subaltern studies and cultural anthropology, eco-nationalism refers to the iconification of native species and landscapes in a way that appeals to a nationalist sentiment.

When discussing eco-nationalism, many writers have noted it is important to understand the difference between ethnic nationalism and civic nationalism. Ethnic nationalism believes that the nation-state should be constructed primarily around a single ethnicity, whereas civic nationalism believes that the nation-state should be constructed around a diversity of people who all share common values, beliefs, and culture. The former tends to be insular, isolationist, nativist, and typically right-wing, while the latter is open, egalitarian, multicultural, and typically more left-wing. Whether ethno nationalist or civic nationalist, when a nationalist group adds an environmentalist dimension to their ideology, they believe the nation-state and its citizens have a duty to protect the environment of the country.

Bioregionalism is the belief that political, cultural, and economic systems are more environmentally sustainable and just if they are organized around naturally defined areas called bioregions. This idea that a state should conform to the natural geography of the land is compatible with the older nationalist concept of a natural border, which also believes that natural geography should determine the borders of a state. Due to the compatibility of these two ideas, Bioregionalism is often a tenet of eco-nationalist thought.

Eco-nationalism can manifest in ecotourism, which can enrich local economies but has garnered criticism from a variety of perspectives. Artistic works that extol the virtues of a nation's natural phenomena, such as the poetry of William Wordsworth or the paintings of the Group of Seven, are another expression of eco-nationalism.

The struggle of the Ogoni people in Ogoniland in coastal south Nigeria against the national government has been characterised as an eco-nationalist movement by Jane Dawson. Following the discovery of oil in the region during the 1960s, the federal government altered how states in Nigeria were budgeted. Before the discovery of oil, a state's budget was based on how much it contributed to the national economy, but after the discovery of oil, the policy became that wealth must be shared out amongst all states. The result of this was that little of the newfound wealth being generated in Ogoniland was reinvested locally, and was instead redistributed to the more politically powerful states in the north of the country. The small percentage of wealth reinvested into Ogoniland was invested into building oil infrastructure, infrastructure which had dire environmental consequences on the region. As a result, Ogoni nationalism took on a distinctive environmentalist dimension in response to these issues.