Marquam Bridge, Double-deck steel cantilever bridge in Portland, Oregon, United States.

The Marquam Bridge is a double-deck steel-truss cantilever bridge carrying Interstate 5 across the Willamette River, from south of downtown Portland to the inner southeast industrial area. Its main span measures 440 feet (130 m), with two side spans of 301 feet (92 m) each. The upper deck carries northbound traffic and the lower deck southbound traffic.

Planning began in 1956 as Oregon's last link in the Interstate Highway System, and the span was named after Philip Marquam, a state legislator and Multnomah County judge who owned much of Marquam Hill. Piers were started in January 1962, and the bridge opened in 1966: the southbound lower deck on October 4 and the northbound upper deck on October 18. It was designed and built by the Oregon Department of Transportation for $14 million, funded by the Federal Highway Transportation Act.

Philip Marquam, the bridge's namesake, was a state legislator and Multnomah County judge who owned much of Marquam Hill, where Oregon Health & Science University and the Veterans Affairs Medical Center now stand. The name was chosen before construction began. Mayor Vera Katz compared the span in 2001 to a wall dividing the city's east and west sides.

The bridge carries only Interstate 5 traffic, with northbound vehicles on the upper deck and southbound on the lower; there is no pedestrian or bicycle access. To see it, walk the Vera Katz Eastbank Esplanade, which runs beneath and parallel to the span on the east bank, or view it from the west-side riverfront south of downtown.

The Marquam was the first Portland bridge to receive a seismic retrofit, in 1995, when Italian-made bearings were fitted to its piers. At the east end of the lower deck a ramp stub was left for the planned Mount Hood Freeway, a project later abandoned.