Operating about 21,000 route miles (34,000 km) of track,[1] it is the leading subsidiary of CSX Corporation, a Fortune 500 company headquartered in Jacksonville, Florida.

[2][3] CSX Corporation was formed in 1980 from the merger of Chessie System and Seaboard Coast Line Industries, two holding companies that controlled railroads operating in the Eastern United States.

Norfolk Southern remains CSX's chief competitor; the two share a duopoly on transcontinental freight rail lines in the east half of the US.

[10] While still independent, the L&N had long standing links to the Atlantic Coast Line, and other railroads in the region began to worry about a combined L&N/SCL system.

Chessie and SCL Industries formally applied for ICC approval of their merger plans in January 1979, causing a rapid reaction from the region's other railroads.

[13] On November 1, 1980, following ICC approval, CSX Corporation officially came into being as the successor of Chessie System and Seaboard Coast Line Industries.

[16] Chessie's public relations staff drafted a number of possible logos for the new railroad, but continued to strike out until it was suggested to combine the letters "C" and "S" in the shape of an X.

When the government identified NS' bid as the winner, CSX realized it faced financial peril from a combined NS/Conrail system.

NS promptly made an offer of its own and began a bidding war with CSX that was only resolved in January 1997 when the competitors struck a deal to split Conrail between them.

[18] On June 23, 1997, CSX and Norfolk Southern Railway (NS) filed a joint application with the Surface Transportation Board for authority to purchase, divide, and operate the assets of the 11,000-mile (18,000 km) Conrail, which had been created in 1976 by bringing together several ailing Northeastern railway systems into a government-owned corporation.

As a result of the transaction, CSX's rail operations grew to include some 3,800 miles (6,100 km) of the Conrail system (predominantly lines that had belonged to the former New York Central Railroad).

The two competitors were unwilling to give one company full control of busy industrial areas in Detroit, Philadelphia, and northern New Jersey (the Chemical Coast).

The RF&P had historically been jointly owned by a number of connecting railroads through a holding company and operated as a bridge line.

All of these owners except the Pennsylvania Railroad and the Southern Railway eventually became part of CSX, and the PRR stake was given up during the bankruptcy of Penn Central.

However, the State of Virginia, which held partial ownership of the RF&P, was displeased with the merger agreement created by CSX.

[20] From the 1930s, the B&O had used part of the Pittsburgh and Lake Erie Railroad (P&LE) main line from McKeesport, Pennsylvania, to West Pittsburg via a trackage rights agreement.

The P&LE remained healthy enough to escape inclusion in Conrail, but a severe downturn in the steel industry in the 1980s crippled the railroad.

The next year, CSX formed the Three Rivers Railway as a subsidiary and purchased several key P&LE lines through it.

In 2017, CSX announced Hunter Harrison would become its new chief executive officer; a settlement with activist investor Paul Hilal and Mantle Ridge.

[25] CSX added five new directors to their board, including Harrison and Mantle Ridge founder Paul Hilal.

On November 30, 2020, CSX Transportation's parent company CSX Corporation announced on social media that they had come to an agreement with Pan Am Systems to purchase New England based Class II Pan Am Railways, pending regulatory approval from the Surface Transportation Board.

[29] As part of the acquisition, Norfolk Southern Railway will gain trackage rights over several CSX lines, and Pan Am Southern, 50 percent owned by Pan Am Railways, will be operated by the Berkshire and Eastern Railroad, a new Genesee & Wyoming subsidiary formed explicitly for this purpose.

[30] On June 28, 2023, CSX and Canadian Pacific Kansas City (CPKC) announced the intention to purchase Meridian and Bigbee Railroad (MNBR).

Currently, CSX traffic bound for Mexico is exchanged with the Union Pacific Railroad in New Orleans, who then takes it to the cross-border gateway in Laredo, Texas, where it is delivered to CPKC.

It also includes conditions protecting employees affected by the line sale, and requires noise mitigation efforts regarding the CSX portion.

[34] A few days before CSX and CPKC officially took over the former M&B line, Schneider National, CSX's one of major intermodal partners and CPKC's main partner, announced that a new interline service connecting the Southeast (Florida and Georgia) with the Texas and Mexico markets via the route between Montgomery and Meridian will be launched beginning in December.

The Juice Train has previously been studied as a model of efficient rail transportation that can compete with trucks and other modes in the perishable-goods trade.

[42] CSX has also obtained a few EMD F40PH-2s that were previously retired from Amtrak, of which are now being used for executive office car service and geometry trains.