Interstate 705 (I-705), also known as the Tacoma Spur, is a short Interstate Highway in Tacoma, Washington, United States. It is a spur route of I-5 that connects the freeway to Downtown Tacoma, Tacoma's waterfront, North Tacoma, and the Tacoma Dome. I-705 was completed in 1988 and is one of the newest portions of the Interstate Highway System in Washington.

I-705 is the shortest Interstate Highway in Washington, at 1.5 miles (2.4 km) in length, and primarily serves as a connector between I-5 and Downtown Tacoma. It begins as a continuation of SR 7 at an interchange with I-5 south of downtown Tacoma, near the Tacoma Dome and America's Car Museum. The freeway passes under I-5, following a gulch south until it terminates at South 38th Street; SR 7 continues beyond Tacoma on Pacific Avenue towards Spanaway and Mount Rainier National Park.

The freeway travels north with an exit to South 26th Street serving the Tacoma Dome and the adjacent Tacoma Dome Station transit complex. I-705 passes over the T Line streetcar near South 25th Street station and continues north to a single-point urban interchange with SR 509 at South 21st Street, which provides access to the University of Washington Tacoma campus and Port of Tacoma. Following a freight railroad, the freeway passes the Washington State History Museum and Union Station near the Bridge of Glass, a pedestrian overpass that crosses I-705 and links the Museum of Glass on the Thea Foss Waterway shore to downtown Tacoma.

The northbound lanes separate near the Bridge of Glass, with one splitting into offramps serving South 15th Street and A Street, the latter of which is also served by a southbound onramp. I-705 then crosses under South 11th Street near the Murray Morgan Bridge and terminates at an onramp from South 9th Street adjacent to Fireman's Park, which cantilevers over the southbound lanes. The freeway continues northwest onto Schuster Parkway, with a separate set of flyover ramps that end at an at-grade intersection with Stadium Way near the Old City Hall.

As a component of the Interstate Highway System, the entirety of I-705 is listed as part of the National Highway System, a national network of roads identified as important to the national economy, defense, and mobility; it is also part of the state government's Highway of Statewide Significance program, recognizing its connection to major communities. The freeway is maintained by the Washington State Department of Transportation (WSDOT), which conducts an annual survey of traffic volume that is expressed in terms of annual average daily traffic. Average traffic volumes on the highway in 2020 ranged from a minimum of 26,000 vehicles at its southern terminus to a maximum of 62,000 vehicles between I-5 and SR 509.

The state government's plans for a regional tollway connecting Tacoma to Seattle and Everett in the early 1950s included a bypass of Downtown Tacoma with several connecting interchanges. The plan later formed the basis of I-5, which would be constructed using funds from the Federal-Aid Highway Act of 1956 instead of requiring a toll. In 1957, city officials from Tacoma proposed the construction of a downtown connector that would travel north from the Pacific Avenue interchange on I-5 (where SR 7 terminates) and improve vehicular access to the central business district. A route along A Street was selected for preliminary studies of either an elevated freeway or one-way couplet.

The opening of the Tacoma Mall along I-5 in 1965 caused a reduction in the number of retailers in Downtown Tacoma, which remained only accessible via local streets from the freeway. The lost business, combined with worsening congestion in Downtown Tacoma, prompted downtown retailers to ask the state government for an improved connection to I-5. The state Department of Highways had advanced their study into a downtown connector as part of SR 509 that would become an eventual freeway link. In 1968, the Department of Highways adopted the routing of a freeway into Downtown Tacoma along the western side of the City Waterway, to be constructed over railroad right of way. The project, then part of a new freeway corridor for State Route 509 through the Port of Tacoma, was approved by the Tacoma City Council in 1971, but further planning was suspended at the time due to funding issues.

In 1978, the American Association of State Highway and Transportation Officials (AASHTO) approved the designation of the Tacoma Spur as I-705. The Federal Highway Administration had tentatively numbered the route as "Interstate 105", but the Washington State Department of Transportation had requested the use of "705" as it would not conflict with SR 105, an existing highway. The Washington State Legislature approved the addition of I-705 into the state highway system in April 1979.