Colas Rail is the dedicated railway infrastructure subsidiary of the Colas Group, a world leader in transport infrastructure and part of the Bouygues Group. Formed in 2008 through the strategic merger of historic rail engineering and contracting entities Seco-Rail (established 1931) and Spie Rail, Colas Rail brings nearly a century of specialized railway construction and maintenance expertise. Headquartered in Puteaux (Paris La Défense), France, the company employs over 6,500 railway specialists operating across more than 25 countries.

As a tier-one turnkey railway contractor, Colas Rail operates across the entire rail lifecycle, from design and procurement to mechanized construction, tracklaying, electrification, signalling installation, testing, commissioning, and long-term maintenance. The firm operates an extensive proprietary fleet of high-output on-track plant, including continuous-action tamping machines, ballast cleaners, rail-laying trains, and catenary installation units.

Colas Rail has delivered landmark high-speed lines worldwide, including the LGV Sud Europe Atlantique (Tours–Bordeaux), LGV Est Européenne, and the Tangier–Kenitra high-speed rail line (Al Boraq) in Morocco. In urban transit, Colas Rail is a key delivery partner on the Grand Paris Express (Lines 15, 16, and 17), the Cairo Metro (Lines 1, 2, 3, and 4) in Egypt, Santiago Metro (Lines 3 and 6) in Chile, the Metro Manila Subway in the Philippines, and the Birmingham Light Rail extension in the United Kingdom. Colas Rail also operates licensed freight haulage services and core track renewal alliances across the UK (Network Rail) and Europe.