The E Line is one of seven RapidRide lines operated by King County Metro in King County, Washington. The E Line began service on February 15, 2014, running between Aurora Village Transit Center in Shoreline and Pioneer Square, Seattle in Downtown Seattle. The line runs mainly via Aurora Avenue N and 3rd Ave.

RapidRide is a network of limited-stop bus routes with some bus rapid transit features in King County, Washington, operated by King County Metro. The network consists of seven routes totaling 76 miles (122 km) that carried riders on approximately 64,860 trips on an average weekday in 2016, comprising about 17 percent of King County Metro's total daily ridership.