A causeway is a berm or other form of solid stable bedding constructed across a body of water as a dry surface for transportation. It is distinguished from a bridge or viaduct in that it does not rest on piers but consists of solid material. It can be built from piled stone, solid concrete, compacted earth between steel retaining walls (a cofferdam), or using other solid or packed materials.

A causeway may form a virtual dam across a body of water, or it may provide for passage of water underneath it through culverts. It can also extend only partway across the water in combination with a bridge.

Solid or packed material supports the dry route across the water. Culverts or an adjoining bridge can permit water passage without turning the solidly bedded portion into a pier-supported bridge.