The Mazda Atenza or Mazda6 is a mid-size car from the Japanese carmaker Mazda. It replaced the Capella/626. As of March 31, 2005, 467,319 Atenza and Mazda6 models had been sold worldwide since introduction.

The model lineup consists of a 4-door sedan, 5-door hatchback, and wagon (estate). Drivetrain combinations include a 2.3 L 4-cylinder L-family engine with a 5-speed manual or 4-speed (with sequential-automatic option, dubbed the "4-Speed Sport AT") automatic transmission. A 3.0 L Ford Duratec-30 V6 engine is also available with a 5-speed manual or 6-speed automatic (with sequential-automatic option, dubbed the "6-Speed Sport AT"). European versions also feature a four-cylinder turbodiesel. In its first years, the Mazda6 came with a 4-speed automatic, 5-speed automatic "AT," and 5-speed manual transmission. During 2005, a 6-speed automatic became available. Final drive is to the front wheels only in most markets, although full-time all wheel drive models are available in Japan and Europe. There is speculation of a larger sedan, the Mazda Mazda9 for the model year 2008 or 2009, to replace the older Mazda 929 and Millenia.

Not all configurations are available in all areas - for example, the Mazda6 as released in Australia was a four-cylinder car only, while the last 626 which it replaced was a four or six cylinder car. This has led to much amusement as to the choice of names. Speaking of which, the name Atenza is used only in Japan - the Mazda6 name is used everywhere else in the world.

Like the 626 before it, Ford is using the Mazda6 "CD3" platform as the basis for a number of other vehicles, including the Ford Fusion, Mercury Milan, Lincoln Zephyr, Lincoln MKX, and a range of SUVs and minivans. Ford also plans to offer a hybrid powertrain on the platform. For its part, Mazda themselves refer to this chassis as either the GG (sedan/hatch) or GY (wagon) series - following the previous 626/Capella in its GF/GW series.

North American Mazda6 production is handled at the AutoAlliance International plant which is a joint venture between Ford and Mazda. The first Mazda6 rolled off this Flat Rock, Michigan assembly line on October 1, 2002, one month after production of the 626 ended. There are also satellite plants building Mazda6 models in China and Thailand.

The 2006 Mazdaspeed 6 is a high-performance version of the Mazda6. It features a turbocharged version of the 2.3 L MZR I4 which produces 274 hp. It has a revised front fascia with a raised hood, a 6-speed transmission, and all wheel drive. Mazda currently has no plans to enter the car into rally racing, and the Mazdaspeed 6 is meant to compete with its Japanese-made turbocharged contemporary, the Subaru Legacy GT and similar sport sedans rather than the smaller, rally-car-derived Subaru Impreza WRX STi and Mitsubishi Lancer Evolution. In some markets such as Australia, it is sold under the name Mazda6 MPS. with MPS standing for Mazda Performance Series, because the MazdaSpeed name has never been introduced to the country.

Originally scheduled to be launched in June 2005, the Mazdaspeed 6 was delayed until November. Now emerging in parts of Canada and the US, the Mazdaspeed6 is getting great feedback. The Mazdaspeed6 comes in two trim levels; the Standard trim with cloth interior and standard key entry and ignition, and the Grand Touring trim with leather interior, keyless entry/igntion, and DVD navigation (Canadian model lacks DVD navigation). It also comes well appointed with an abundance of brushed metal and faux silver-finished wood trim. Automatic climate control is standard as is a 300 watt BOSE stereo boasting 8 speakers and a 10" subwoofer in addition to an in-dash 6 CD disc changer. As an included feature, the Grand Touring trim also has a sunroof with moonroof feature.

Performance of the Mazdaspeed6 is outstanding. Acceleration experienced when driving the Mazdaspeed6 is more often seen in cars with substantially higher price tags and two fewer seats. Although Mazda estimates 0-60 MPH times to be 6.6 seconds, recent independent tests by automotive journalists have suggested that the actual numbers might range between 5.6-6 seconds (with DSC deactivated). The power band is sufficiently broad reaching its peak at 2500 RPM and continuing unabated to well over 5000 RPM. As a result, power is readily available in any gear as long as the RPM are kept above 3000 RPM. Below 3000 RPM, however, a slight amount of turbo lag is noticeable.