A multi-billion dollar complex of coastal construction protects the delta-estuarine region of the south-west Netherlands from a repeat of the 1953 storm-surge flooding that killed 1835. Eight documented storm-surge flood disasters date back to 1717. The Delta Project became effective in terms of flood protection in 1986, but sections of it are still under construction. One of the world's greatest civil-engineering projects, its 11 major and multiple secondary components have the function of (1) closing off three main estuaries which shorten the coastline by approximately 720 km, (2) creating a non-tidal waterway, the Scheldt-Rhine link, which facilitates inland shipping between Antwerp and Rotterdam (120 km), two of the largest ports in the world, and (3)ensuring the partial environmental preservation of the Delta area. This case history addresses geology and foundation problems, planning and construction sequence, site investigation and foundation preparation, methods of construction, and foundation/structural interaction. The main focus is the megascale control barrier completed in 1986 across the 7.5 km-wide mouth of the Eastern Scheidt estuary, the most difficult and by far the most costly section of the project. Here, and in other parts of the Delta area, strong tidal currents and highly-variable geological materials with relatively poor engineering properties were responsible for foundations requiring up to 80 percent of the total construction time. The new techniques developed on the Project have world-wide application to future coastal and offshore construction.