The world's forests hold importance for all of their inhabitants as well as for the overall health of the planet. The benefits of forests to society and to the diversity of life make it vital that they be protected from deforestation and other potential negative impacts of civilization.

Forests thrive in diverse climatic regions throughout the world, and can be categorized by their locations and elevations.

Forests are major contributors to the Earth's ability to maintain its climate, by the global impact of their photosynthesis. They are a natural defense against climate change, removing the greenhouse gas carbon dioxide and generating oxygen. This assists in purifying the atmosphere and controlling rising temperatures. Deforestation negates these benefits.

In addition to assisting in climate control, forests have other ecological benefits. They prevent erosion by reducing the rainfall's force on the soil's surface and by absorbing water and not allowing it to directly run off and remove topsoil. Forests also act as water filters, collecting and storing water and recharging underground aquifers. Tropical montane forests are especially important to watersheds. Forests also increase the atmosphere's humidity by transpiration, which affects temperature and rainfall.

Forests contain a greater range of biodiversity than any other ecosystems on earth. Only a fraction of the species found in forests have been examined and studied. A single massive tree in the Amazon rainforest can be home for thousands of species. The wide variety of trees and plants found in tropical forests comprises particularly intensive biodiversity. This biodiversity is be important on its own terms in ways we may not currently understand, as interdependent species have evolved over millions of years to interact and flourish.

Humankind derives many benefits from forest ecosystems. Many medicines and pharmaceuticals have been discovered in plants native to forests. Local communities survive on plants and animals culled from the forests. Products that modern society depends on such as wood, paper and bamboo all originate from forest ecosystems. Many other desirable products such as spices, gums and dyes are also found in forests around the globe. Forests are important to humans for aesthetic reasons as well, and ecotourism is one way to use and promote the protection of forests in a sustainable manner.