Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to (typically a steep, near-vertical or vertical slope). They are used to bound soils between two different elevations often in areas of terrain possessing undesirable slopes or in areas where the landscape needs to be shaped severely and engineered for more specific purposes like hillside farming or roadway overpasses.

A retaining wall is designed to hold in place a mass of earth or the like, such as the edge of a terrace or excavation. The structure is constructed to resist the lateral pressure of soil when there is a desired change in ground elevation that exceeds the angle of repose of the soil.

Every retaining wall supports a "wedge" of soil. The wedge is defined as the soil which extends beyond the failure plane of the soil type present at the wall site, and can be calculated once the soil friction angle is known. As the setback of the wall increases, the size of the sliding wedge is reduced. This reduction lowers the pressure on the retaining wall

When built properly, retaining walls are an integral part of the house structure that last a lifetime. Retaining walls are can be made from a variety of different materials. A very popular and economical way of installing retaining walls is to use a mortar-less interlocking block system known as gravity walls. These walls have no cement based products incorporated within their construction. Usually, retaining walls sit on a compacted leveled gravel bed with the first course of block below grade. Another rule of thumb is to bury an inch of block per course of wall. These walls are typically very heavy with a lip or pin to interlock each block, and are structured so that each course of wall works with gravity. Once the wall reaches 4 feet in height, a geo grid is required, which is a plastic netting that is sandwiched between the block and goes into the earth 3 feet.