The Dom Luís I (or Luiz I) Bridge (Portuguese: Ponte Luís I or Luiz I) is a metal arch bridge that spans the Douro River between the cities of Porto and Vila Nova de Gaia inPortugal. At the time of construction its span of 172 m was the longest of its type in the world.

The government held a competition for the construction of a metallic bridge over the Douro River on a site that was adjacent to an existing bridge that it would replace. Téophile Seyrig had engineered the D. Maria Pia Bridge project nearby, whilst working as a partner of Gustave Eiffel. He now took sole responsibility for the new, major Luís I Bridge. The construction was begun in 1881 and the bridge opened on 31 October 1886 (the upper deck; the lower deck opened in 1887).