The The Yellow Line, locally still called by its original name, the Skokie Swift (and somewhat also by the CTA) is the Chicago 'L's only line that is always a shuttle, although it is quite a long shuttle at 4.7 miles, the Purple Line, Evanston Branch is shorter at 3.9 miles but has 9 stations. Until the Oakton/Skokie intermediate stop opened on April 30, 2012 the line was a true shuttle with just two stations, one at each end (Dempster/Skokie was just called Skokie). The present line was inaugurated as a 'demonstration project' under the National Housing Act of 1961 to see if parking was provided in a suburban community suburbanites would park their cars and take a high speed transit line into the downtown of a city. (The same federal housing act provided funding to build the Jersey Avenue Park & Ride Station). A brochure from the inauguration of the line calls it 'The Worlds Fastest Rapid Transit: Five miles in 6½ minutes' The swift opened on Monday April 20, 1964 and was originally supposed to run weekdays only but ridership was nearly five times the anticipated number of passengers that Saturday service was added for the first weekend and continued. A ride cost 45 cents compared to a quarter for rides within the City of Chicago.Sunday service was never offered.

The line's other unique feature was that most of the route used overhead catenary lines because of its legacy from the North Shore Interurban Line. The line operated with its own uniquely modified fleet of cars (about ten) that had pantographs and third rail shoes with the switch happening in the middle of trips. This was the case until September 2004 when a new third rail was installed and activated. The catenary wires were then removed in November 2004. Saturday service was discontinued under CTA budget cuts as of February 15, 1992, and trains ran weekdays only except for a demonstration of weekend service over the holiday shopping season in December 2002. In March 2008 CTA finally reinstated Saturday service and began Sunday service for really the first time. Today trains run 7 days per week from 5:00am on Weekdays, 6:30am on weekends to 11:00pm daily (service hours are often extended for special events in downtown Chicago). The shuttle has the least frequent service of any CTA Line, except for on the Green Line's two branches, with a 15 minute base frequency expanded to every 10 minutes during weekday rush hours.

The demonstration line didn't materialize out of thin air in 1964. It follows the route used by the North Shore Interurban Line that opened on March 28, 1925, and was built together by both the North Shore Interurban and the Chicago Rapid Transit Company (predecessor of the CTA) which operated transit service as far as Dempster on the route of today's Skokie Swift with 7 intermediate stations. Transit Service on the branch was one of the CTA's first service cuts after it took over operations. It was discontinued on March 26, 1948. The North Shore Interurban continued operations, making stops at just Howard and Dempster on its trips to and from Milwaukee to the Loop (via the North Side Main Line shared with 'L' trains) until it finally abandoned operations in 1963. The tracks were never abandoned and a short portion of this historic line was then reinstated with the Skokie Swift in 1964.