Metra (reporting mark METX) is the primary commuter rail system in the Chicago metropolitan area serving the city of Chicago and its surrounding suburbs via the Union Pacific Railroad, BNSF Railway, and other railroads. The system operates 243 stations on 11 rail lines. It is the fourth busiest commuter rail system in the United States by ridership and the largest and busiest commuter rail system outside the New York City metropolitan area. In 2024, the system had a ridership of 34,877,600, or about 174,400 per weekday as of the second quarter of 2025. The estimated busiest day for Metra ridership occurred on November 4, 2016—the day of the Chicago Cubs 2016 World Series victory rally, with a record 460,000+ passengers.

Metra is the descendant of numerous passenger rail services dating to the 1850s. The present system dates to 1974, when the Illinois General Assembly established the Regional Transportation Authority (RTA) to consolidate transit operations in the Chicago area, including commuter rail as a public utility. The RTA's creation was a result of the anticipated withdrawal of commuter service operated and owned by various private railroad companies in the 1970s. In a 1983 reorganization, the RTA placed commuter rail under a newly formed Commuter Rail Division, which branded itself as Metra in 1985. Freight rail companies still operate four of Metra's routes under purchase-of-service agreements. Metra owns all rolling stock and is responsible for all stations along with the respective municipalities. Since its inception, Metra has directed more than $5 billion into the commuter rail system of the Chicago metropolitan area alongside the CTA. In January 2023, Metra rolled out a new real-time train tracking website to allow passengers greater visibility into their commute.

Since the 19th century, Chicago has been a major hub in the North American rail network. It has more trackage radiating in more directions than any other city in North America. Railroads set up their headquarters in the city and Chicago became a center for building freight cars, passenger cars and diesel locomotives. Early commuter services were run by the Chicago, Burlington and Quincy, Chicago and North Western, and Milwaukee Road.

By the 1930s, Chicago had the world's largest public transportation system, but commuter rail services started to decline. By the mid-1970s, the commuter lines faced an uncertain future. The Burlington Northern, Milwaukee Road, Chicago and North Western and Illinois Central had been losing money for several years, and were using trainsets with passenger cars dating as far back as the 1920s.

To provide stability to the commuter rail system, the Illinois General Assembly formed the Regional Transportation Authority in 1974. Its purpose was to fund and plan the Chicago region's public transportation. After initially using second-hand equipment, the RTA took delivery of the first new EMD F40PH locomotives in 1976. That F40PH fleet is still in service today. The companies that had long provided commuter rail in the Chicago area continued to operate their lines under contract to the RTA.

Less than a decade later the RTA was already suffering from ongoing financial problems. Additionally, two rail providers, the Rock Island Line and the Milwaukee Road, went bankrupt, forcing the RTA to create the Northeast Illinois Regional Commuter Railroad Corporation to operate their lines directly in 1981 and 1982 respectively. In 1983 the Illinois Legislature reorganized the agency. That reorganization left the Regional Transportation Authority in charge of day-to-day operations of all bus, heavy rail and commuter rail services throughout the Chicago metropolitan area. It was also responsible for directing fare and service levels, setting up budgets, finding sources for capital investment and planning. A new Commuter Rail Division was created to handle commuter rail operations; along with CTA and Pace, it was one of RTA's three "service boards".

The board of the RTA Commuter Rail Division first met in 1984. In an effort to simplify the operation of commuter rail in the Chicago area, in July 1985 it adopted a unified brand for the entire system–Metra, or Metropolitan Rail. The newly reorganized Metra service helped to bring a single identity to the many infrastructure components serviced by the Regional Transportation Authority's commuter rail system. However, the system is still legally known as the Commuter Rail Division of the RTA.

Today, Metra's operating arm, the Northeast Illinois Regional Commuter Railroad Corporation, operates seven Metra owned routes. Four other routes continue to be operated by Union Pacific (formerly Chicago & North Western) and BNSF (formerly Burlington Northern) under contract to Metra. Service throughout the network is provided under the Metra name (in keeping with Metra's goal of providing a single identity for all commuter rail in the region). Metra also owns all rolling stock, controls fares and staffing levels, and is responsible for most of the stations. However, the freight carriers who operate routes under contract use their own employees and control the right-of-way for those routes.