A valley is an area of elongated lowland, typically surrounded by much higher hills or mountains. Valleys are one of many geological features which make up the surface of the Earth, and they are of special interest and importance to humans, thanks to the fact that valleys have a number of uses. Chances are high that there is a valley in your area, since this landform is quite abundant.

Valleys form in a number of ways, with some geologists breaking up valleys by type on the basis of how they are formed. A rift valley is formed through separation of the Earth's crust, caused by violent tectonic movements; a notable example of a rift valley is the Great Rift Valley in Africa. A glacial valley is a valley which has been formed by a glacier; glacial valleys are especially common in Europe, and they have a distinctive U-shaped profile when viewed in cross-section. River valleys are formed through the slow process of erosion over the course of centuries, and they typically have a V-shaped profile.

Unlike a canyon, a valley is broad, with a large area of valley floor, rather than a narrow profile. Valleys are generally easy to navigate, and they tend to have a different climate than the surrounding area. It is also common for a valley to have rich deposits of alluvial mud, making it ideal for agriculture. As a result, many human civilizations have settled in valleys, taking advantage of the rivers which often wind through valleys as a source of water.

Viewed from overhead, a valley often stands out from the surrounding terrain because it has different plant life than the surrounding hills and mountains. This can cause a valley to appear lighter in color than the surrounding land, especially when the valley has been cultivated or shaped by humans in some way. The sloping sides of the valley also tend to give it away, leading the eye to the deepest part of the valley floor.

Valleys also have unique weather, because their sloping sides can trap hot air, causing valleys to warm up considerably in the summer. A valley may also act to trap fog and low-lying clouds, creating a very misty environment. Valley dwellers often bemoan their unique weather, with some people choosing to live on the sloping sides of the valley to avoid the stagnant weather conditions which may abound at the valley floor.