A bridge is a structure built to cross an obstacle, crossing a physical obstacle without closing a road underneath, such as a water, valley, or road. There are many different designs, each with a specific purpose and for different situations. The design of a bridge depends on the function of the bridge, the nature of the terrain in which it is built and anchored, the materials used to make it, and the funds available to build it.

Bridges can be classified by the distribution of tension, compression, bending, torsion and shear in their structures. Most bridges will use all the main forces to some extent, but only a few will dominate. The separation of forces may be clear. In suspension or cable-stayed bridge, the shape and position of tension components are different. In other cases, such as in trusses, forces can be distributed across a large number of members.