Temperate deciduous or temperate broadleaf forests are a variety of temperate forest mostly composed of deciduous trees that lose their leaves each winter. They represent one of Earth's major biomes, making up 9.69% of global land area. These forests are found in areas with distinct seasonal variation that cycle through warm, moist summers, cold winters, and moderate fall and spring seasons. They are most commonly found in the Northern Hemisphere, with particularly large regions in eastern North America, East Asia, and a large portion of Europe, though smaller regions of temperate deciduous forests are also located in South America. Examples of trees typically growing in the Northern Hemisphere's deciduous forests include oak, maple, basswood, beech and elm, while in the Southern Hemisphere, trees of the genus Nothofagus dominate this type of forest. Temperate deciduous forests provide several unique ecosystem services, including habitats for diverse wildlife, and they face a set of natural and human-induced disturbances that regularly alter their structure.

Located below the northern boreal forests, temperate deciduous forests make up a significant portion of the land between the Tropic of Cancer (23${\displaystyle {\tfrac {1}{2}}}$°N) and latitudes of 50° North, in addition to areas south of the Tropic of Capricorn (23${\displaystyle {\tfrac {1}{2}}}$°S). Canada, the United States, China, and several European countries have the largest land area covered by temperate deciduous forests, with smaller portions present throughout South America, specifically Chile and Argentina.

Temperate conditions refer to the cycle through four distinct seasons that occurs in areas between the polar regions and tropics. In these regions where temperate deciduous forest are found, warm and cold air circulation accounts for the biome's characteristic seasonal variation.

The average annual temperature tends to be around 10 °Celsius, though this is dependent on the region. Due to shading from the canopy, the microclimate of temperate deciduous forests tends to be about 2.1 °Celsius cooler than the surroundings, whereas winter temperatures are from 0.4 to 0.9 °Celsius warmer within forests as a result of insulation from vegetation strata.

Annually, temperate deciduous forests experience approximately 750 to 1,500 millimeters of precipitation. As there is no distinct rainy season, precipitation is spread relatively evenly throughout the year. Snow makes up a portion of the precipitation present in temperate deciduous forests in the winter. Tree branches can intercept up to 80% of snowfall, affecting the amount of snow that ultimately reaches and melts on the forest floor.

A factor of temperate deciduous forests is their leaf loss during the transition from fall to winter, an adaptation that arose as a solution for the low sunlight conditions and bitter cold temperatures. In these forests, winter is a time of dormancy for plants, when broadleaf deciduous trees conserve energy and prevent water loss, and many animal species hibernate or migrate. Preceding winter is fruit-bearing autumn, a time when leaves change color to various shades of red, yellow, and orange as chlorophyll breakdown gives rise to anthocyanin, carotene, and xanthophyl pigments.

Besides the characteristic colorful autumns and leafless winters, temperate deciduous forests have a lengthy growing season during the spring and summer months that tends to last anywhere from 120 to 250 days. Spring in temperate deciduous forests is a period of ground vegetation and seasonal herb growth, a process that starts early in the season before trees have regrown their leaves and when ample sunlight is available. Once a suitable temperature is reached in mid- to late spring, budding and flowering of tall deciduous trees also begins. In the summer, when fully-developed leaves occupy all trees, a moderately-dense canopy creates shade, increasing the humidity of forested areas.

Though there is latitudinal variation in soil quality of temperate deciduous forests, with those at central latitudes having a higher soil productivity than those more north or south, soil in this biome is overall highly fertile. The fallen leaves from deciduous trees introduce detritus to the forest floor, increasing levels of nutrients and organic matter in the soil. The high soil productivity of temperate deciduous forests puts them at a high risk of conversion to agricultural land for human use.