The St. Charles Streetcar Line is a historic streetcar line in New Orleans, Louisiana. Running since 1835, it is the oldest continuously operating streetcar line in the world. It is operated by the New Orleans Regional Transit Authority (RTA). Officially the St. Charles Streetcar line is designated as Route 12, and it runs along its namesake, St. Charles Avenue. It is the busiest route in the RTA system as it is heavily used by local commuters and tourists. On most RTA maps and publications, it is denoted in green, which is also the color of the streetcars on this line.

Streetcars in New Orleans have been an integral part of the city's public transportation network since the first half of the 19th century. The longest of New Orleans' streetcar lines, the St. Charles Avenue line, is the oldest continuously operating street railway system in the world. Today, the streetcars are operated by the New Orleans Regional Transit Authority (RTA).