Karst is a terrain distinguished by its underground drainage, natural cavities and sinkholes. New subsidence sinkholes (both dropout and suffosion) formed within the soil cover constitute the main karst geohazard. Nearly all are induced by increased drainage inputs or by water table decline, and control of the drainage is the primary means of reducing their hazard. Cave collapse and the development of collapse sinkholes in bedrock are less common, and the stability of a cave roof that is thicker than its width means that only those caves at shallow depth create any hazard. Predictions of the locations of caves or potential sinkhole sites are next to impossible, geophysical searches have severe limitations and borehole searches can incur significant costs. Consequently, controlling the drainage on construction projects is usually the most cost-effective means of minimizing the karst geohazard.