The list of the world's tallest bridges ranks bridges around the world by the height of their structure. The structural height of a bridge is the maximum vertical distance from the uppermost point of a bridge, such as the top of a bridge tower in a suspension bridge, down to the lowest visible point of a bridge, where its piers emerge from the surface of the ground or water. Structural height should not be confused with deck height, which measures the maximum vertical drop distance from the bridge deck (the road bed of a bridge) down to the ground or water surface beneath the bridge span. A separate list of the world's highest bridges ranks bridges by deck height.
The rankings of the world's tallest and highest bridges differ in part because some of the highest bridges are built across deep valleys gorges. The Sidu River Bridge in Hubei Province of China is a suspension bridge that spans a deep river gorge. The bridge's two towers, built on either rim of the gorge, are not tall enough for the bridge structure to be counted among the world's tallest, but thanks to the depth of the river gorge, the deck height of the Sidu River Bridge is at least 496 m (1,627 ft), making the bridge the highest in the world. The Millau Viaduct, a cable-stayed bridge that spans the Tarn River Valley in southern France, is a bridge that is both tall (in structural height) and high (in deck height). The viaduct's bridge deck soars 270 m (890 ft) above the valley floor, making the bridge the tenth highest in the world. Unlike the Sidu River Bridge, tallest of the Millau Viaduct's towers (also referred to as mast pylons) is planted in the valley floor and gives the structural height of 343 m (1,125 ft), making it the tallest bridge in the world.