The South Shore Line is an electrically powered interurban commuter rail line operated by the Northern Indiana Commuter Transportation District (NICTD) between Millennium Station in downtown Chicago and the South Bend International Airport in South Bend, Indiana, United States. The name refers to both the physical line and the service operated over that route. The line was built in 1901–1908 by predecessors of the Chicago South Shore and South Bend Railroad, which continues to operate freight service. Passenger operation was assumed by the NICTD in 1989, who also purchased the track in 1990. The South Shore Line is one of the last surviving interurban trains in the United States. In 2023, the system had a ridership of 1,406,900, or about 5,000 per weekday as of the fourth quarter of 2023.

Railway electrification is the use of electric power for the propulsion of rail transport. Electric railways use either electric locomotives, electric multiple units or both. Electricity is typically generated in large and relatively efficient generating stations, transmitted to the railway network and distributed to the trains. Some electric railways have their own dedicated generating stations and transmission lines, but most purchase power from an electric utility. The railway usually provides its own distribution lines, switches, and transformers.