Cardiff Blues (Welsh: Gleision Caerdydd) are one of the four professional Welsh rugby union teams. Based in Cardiff, the capital of Wales, the team play at Cardiff Arms Park and are owned by Cardiff Rugby Football Club.

Cardiff Blues are responsible for developing rugby union in the city of Cardiff, Vale of Glamorgan, parts of the old county of Mid Glamorgan and Southern Powys.

The Cardiff Blues compete in the Magners League, which includes teams from the Celtic nations of Ireland, Scotland and Wales. In addition, Cardiff Blues compete in the Anglo-Welsh EDF Energy Cup and European Heineken Cup. The club have qualified for the Heineken Cup every season, but have yet to win honours in one of their competitions.

The team's main sponsor is currently the low cost airline Bmi baby. The Cardiff Blues kit is manufactured by Canterbury of New Zealand.