The MAX Red Line is a light rail line serving the Portland metropolitan area in the U.S. state of Oregon. Operated by TriMet as part of the MAX Light Rail system, it is an airport rail link connecting Beaverton, Portland City Center, and Northeast Portland to Portland International Airport. The Red Line serves 27 stations; it interlines with the Blue Line and partially with the Green Line from Beaverton Transit Center to Gateway/Northeast 99th Avenue Transit Center and then branches off to Portland Airport station. Service runs for 22 hours per day with headways of up to 15 minutes. The Red Line carried an average 10,310 passengers per weekday in September 2021, the second-busiest after the Blue Line.

The Tri-County Metropolitan Transportation District of Oregon (TriMet) is a transit agency that serves most of the Oregon part of the Portland metropolitan area. Created in 1969 by the Oregon legislature, the district replaced five private bus companies that operated in the three counties: Multnomah, Washington, and Clackamas. TriMet began operating a light rail system, MAX, in 1986, which has since been expanded to five lines that now cover 59.7 miles (96.1 km). It also operates the WES Commuter Rail line since 2009. It also provides the operators and maintenance personnel for the city of Portland-owned Portland Streetcar system. In 2023, the system had a ridership of 62,055,600, or about 196,900 per weekday as of the fourth quarter of 2023.