The Interstate Bridge (also Columbia River Interstate Bridge, I-5 Bridge, Portland-Vancouver Interstate Bridge, Vancouver-Portland Bridge) is a pair of nearly identical steel vertical-lift, Parker through-truss bridges that carry Interstate 5 traffic over the Columbia River between Vancouver, Washington and Portland, Oregon in the United States.

The present-day northbound bridge opened to traffic in 1917 as a single bridge carrying two-way traffic. A second twin bridge, which carries southbound traffic, opened in 1958. The twin bridges are each over 3,500 feet (1,067 m) long and carry three lanes of traffic. The bridges handle a combined 130,000 vehicles daily. It was added to the National Register of Historic Places in 1982, as the "Portland–Vancouver Highway Bridge".

Since 2005, several proposals for replacing the bridge have been produced and debated. The bridge is considered responsible for traffic congestion of both road and river vehicles. Plans for a replacement bridge, known as the Columbia River Crossing (CRC) project, estimated to cost at least $3.4 billion, had come together by 2012 after many delays, but were very controversial, with both strong support and strong opposition. In late June 2013, the CRC project was canceled, after the Washington state legislature declined to authorize funding for the project. The Interstate Bridge Replacement Program, a joint effort between ODOT, WSDOT, Federal Highway Administration, Federal Transit Administration, Metro, Southwest Washington Regional Transportation Council, the cities of Portland and Vancouver, the Port of Portland, and the Port of Vancouver USA, was relaunched in 2017.

Before a permanent crossing existed between Portland and Vancouver, there was an overcrowded ferry system operated by Pacific Railway, Light & Power Co.

Plans for the original bridge began as early as 1912, with local efforts leading to an initial survey and bond measures totaling $2,000,000; $1.5 million contributed from Portland, and $500,000 from Vancouver. Waddell & Harrington were retained as the project's consulting engineers. Construction on the bridge began in March 1915, and the structure opened on February 14, 1917 at a final cost of $1.75 million (equivalent to $43 million in 2024), which was shared between Clark and Multnomah counties. Clark County paid $500,000 and Multnomah County paid $1.25 million—probably proportional to population.

The first bridge has a total of 13 steel spans, with three measuring 275 feet (84 m) in length and the remaining ten spans 265 ft (81 m) each. Piers sit atop pile caps on wooden pilings approximately 70 feet deep. One of the 275-foot (84 m) spans is the lift span for allowing river traffic under the bridge. The lift span is capable of moving 136 ft (41 m) vertically, and provides 176 ft (53.6 m) of clearance below when fully raised. The towers are 190 ft (57.9 m) tall, above the roadway.

The original paved roadway was 38 ft (11.6 m) wide and had a 5 ft (1.52 m) wide sidewalk. It was the first automobile bridge across the river between Washington and Oregon, and the second to span the river at all, after the Wenatchee Bridge of 1908. It was originally a toll bridge costing 5¢ per vehicle or per horse and rider, equivalent to $1.23 in 2024. In 1928 the states of Washington and Oregon jointly purchased the bridge from the counties and discontinued tolling the following year. The Oregon Department of Transportation became the lead agency responsible for the maintenance and operations of the structure.

Electric streetcars operated across the bridge from opening day in 1917 until 1940. The bridge's deck carried dual gauge track, to accommodate both Vancouver's standard gauge cars and Portland's 3 ft 6 in (1,067 mm) gauge cars. Before the bridge, Portland had had a Vancouver streetcar line since 1893, but it ran to Hayden Island, where passengers transferred to a ferry owned by the street railway company to continue across the river to Vancouver. Streetcar service across the Interstate Bridge ended on September 3, 1940.