A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic rift or fault. This action is manifest as crustal extension, a spreading apart of the surface which is subsequently further deepened by the forces of erosion. When the tensional forces are strong enough to cause the plate to split apart it will do so such that a center block will drop down relative to its flanking blocks, forming a graben. This creates the nearly parallel steeply dipping walls. This feature is the beginning of the rift valley. As this process continues, the valley gets wider and wider until it becomes a large basin that fills with sediment from the rift walls and the surrounding area. One of the better long term examples of this process is the Basin and Range province in Nevada and Utah. Rifts can occur at all elevations, from the sea floor to plateaus and mountain ranges. They can occur in continental crust or in oceanic crust. Rift valleys are often associated with a number of adjoining subsidiary or co-extensive valleys which are typically considered geologically part of the principal rift valley.

Rift Valley Province of Kenya, bordering Uganda, is one of Kenya's seven administrative provinces outside Nairobi. Rift Valley Province is the largest and one of the most economically important provinces in Kenya. It is dominated by the Kenya Rift Valley which passes through it and gives the province its name. According to the 1999 Census, the province covers an area of 173,854 square kilometres (42,960,000 acres; 67,125 sq mi) and has a population of 8,786,300 inhabitants (2007),^{[citation needed]} making it the largest and most populous province in the country. The capital is the town of Nakuru.

The Great Rift Valley runs south through Kenya from Lake Turkana in the north and has several unique geographical features, including the Elgeyo escarpment which is a popular tourist attraction.

Apart from the Rift Valley itself, the area has other important geographic features such as: the extinct volcanoes Mount Longonot and Mount Suswa and Lake Baringo, Lake Bogoria, Lake Magadi, Lake Nakuru, Lake Naivasha, the Suguta Valley, and Lake Turkana.