Drilled shafts, also called caissons and rock socketed drilled shafts, are typically high-capacity cast-in-place deep foundation elements. The selection of the foundation system is generally based upon several factors. For example, drilled shafts are chosen in urban settings where vibration cannot be tolerated or where shallow foundations cannot develop sufficient capacity. Their use as structural support has increased due to heightened lateral strength and seismic requirements for bridge foundations. They are particularly advantageous where enormous lateral loads from extreme-event limit states govern bridge foundation design length. Relatively new developments in design and construction methods of shafts have provided considerably more economy to their use in all settings. Additional applications include providing foundations for buildings, industrial installations, jetties and docks, high mast lighting, cantilevered signs, cellular phone and communication towers. In many instances, a single drilled shaft can replace a cluster of piles eliminating the need (and cost) for a pile cap.