Ecologism, or Green Theory, focuses on the relationship between people and the environment, transcending traditional political thought by viewing humanity as part of a larger ecosystem. Emerging as an ideology in the 1970s, it built upon earlier concerns for nature. The key concept of eco-centrism, which forms the basis of Deep Ecology, asserts that humans are part of the natural world and should not hold an anthropocentric (human-centered) view, deeming human life no more important than other species.

The concept of eco-centrism led to a split in the environmental movement: some advocated for policy changes within existing systems, while deep ecologists called for fundamental societal change. Environmentalism is a broad term for those raising green issues, typically utilizing an anthropocentric approach. This includes 'light green' environmentalism (individual actions) and 'bright green' environmentalism (technological solutions) often associated with liberalism.

Various political ideologies view environmentalism differently. Marxist-influenced socialists blame capitalism for environmental degradation. Anarchism, exemplified by Peter Kropotkin's theory of mutual aid, has a long-standing interest in the natural world, often advocating for rural communal living. Conservatives, on the other hand, see environmental preservation as part of their obligation to conserve existing society.

Deep ecology, founded on eco-centrism, aims to transform humanity's worldview and relationship with nature. It rejects a mechanistic, 'Newtonian-Cartesian' understanding of the world, advocating instead for a holistic approach inspired by philosophies like Buddhism, often questioning the scientific method. Sustainability is central to deep ecology, leading to critiques of modern materialism and calls for limited or zero growth, and sometimes even population control measures.

Deep ecologists argue that nature possesses intrinsic value, independent of human utility or morality, potentially rooted in religious or ethical beliefs. Ecologism is unique due to the divergence between its two main strands: environmentalism (focused on policy) and deep ecology (a more intellectual, academic pursuit). Despite this, the increasing importance of green issues suggests ecologism will become more relevant in the future.