The Mazda Atenza or Mazda 6 is a mid-size car produced by the Japanese car manufacturer Mazda since 2002. The name Atenza is used only in Japan with the Mazda 6 moniker used everywhere else in the world. The Atenza/Mazda 6 replaced the Capella/626, and has sold over one million units worldwide since its introduction, hitting that sales milestone faster than previous Mazdas.

The Mazda Atenza was the first of the new generation of 'Stylish', 'Insightful', and 'Spirited' range from Mazda. It was followed by the Mazda 2 in December 2002, RX-8 in August 2003, Mazda3 in January 2004, Mazda5 in the summer of 2005, MX-5 in October 2005, and Mazda CX-7 in November 2006.

The Mazda Atenza is currently raced in the SCCAPro Racing Speed World Challenge Touring Car Series. Mazda finished first in the manufacturer's championship standings. Mazda Atenza/6 drivers also finished first and second in the Touring Car driver points.

The model lineup consists of a four-door sedan, a five-door liftback and a five-door station wagon, marketed in North America as the "Sport Sedan", "5-Door" and "Sport Wagon", respectively. In Australia, the lineup starts with Limited, available only as a sedan. Then comes the Classic, available in sedan, hatch or wagon. The Luxury model is next available in sedan and hatch versions. Topping the range is the Luxury Sports model, available only as a hatch. When it arrived in North America, it was first sold as a 2003 model in the United States and as a 2004 model in Canada. In Europe, the luxury sports model was available as a 136hp (101kW) direct injection turbodiesel ("DITD") station wagon up until 2007. As of 2008, the European Mazda catalog lists only the "Sport" version of the 146hp (109kW) turbodiesel station wagon, while the "Luxury Sport" version has been dropped.