On a world scale, the dissolution of limestone and gypsum by natural waters creates extensive karst landforms that can be very difficult ground for civil engineers. Caves threaten foundation integrity, notably where their width is greater than their roof thickness. Sinkholes pose many problems, and are classified into six types, including subsidence sinkholes formed in soil cover within karst terrains. Rockhead morphology varies from uniform to pinnacled, also creating difficult ground to excavate or found upon. A proposed engineering classification of karst defines various complexities of ground conditions by the geohazards that they provide, mainly the caves, sinkholes and rockhead relief. Ground investigation techniques and foundation design philosophies are considered so that they are appropriate to the ground conditions provided by the different classes of karst.