In construction or renovation, underpinning is the process of strengthening the foundation of an existing building or other structure. Underpinning may be necessary for a variety of reasons:

• The original foundation isn't strong or stable enough.
• The usage of the structure has changed.
• The properties of the soil supporting the foundation may have changed or were mischaracterized during design.
• The construction of nearby structures necessitates the excavation of soil supporting existing foundations.
• To increase the depth or load capacity of existing foundations to support the addition of another storey to the building.
• It is more economical, due to land price or otherwise, to work on the present structure's foundation than to build a new one.
• Earthquake, flood, drought or other natural causes have caused the structure to move, requiring stabilisation of foundation soils and/or footings.