Epsilon is General Motors' mid-size front-wheel drive automobile platform. The architecture was a multi-division project of GM North America, Opel and Saab,^[2] and debuted in the 2002 Opel Vectra and 2003 Saab 9-3. Since this platform falls squarely in the center of the worldwide automobile market, GM plans to produce a great many Epsilon vehicles with over a dozen variations. As of 2005^[update], it was GM's highest volume worldwide platform. Even after the dissolution of the GM/Fiat partnership, both companies retain the rights to continue developing Epsilon-derived models.

A total of 16 different models have made use of the GM Epsilon platform, some of which remain in production 19 years after the platform debuted.

GM's Epsilon platform replaced the N platform in the US, and replaced the GM2900 platform elsewhere. Vehicles of this platform generally carry the symbol "Z" in the fourth digit of their VINs.

When the platform debuted, there was talk of an "Epsilon Wide" derivative, which was supposed to have provided the underpinnings for the Buick LaCrosse and Saab 9-5. However, the program was cancelled and the LaCrosse was put on the W platform, and the 9-5 was given a quick refresh for the 2006 model year. ^{[citation needed]}

The Epsilon platform is a midsize front-driver promising a 200 percent improvement in rigidity, with aluminum suspension components—MacPherson struts in front and a four-link independent arrangement in the rear, and four-wheel disc brakes. Many of the Epsilon vehicles use the Ecotec Inline-four engines and both the High Value and High Feature V6 engines.

The refreshed 2008 SAAB 9-3 debuted with an advanced version of all-wheel-drive it dubbed XWD, finally giving a definitive answer to rumors about the platform's ability to support AWD, which had been around since the debut of the platform.

The Lambda and Theta Premium crossover platforms are derived from Epsilon. ^{[citation needed]}

A new version of the Epsilon, dubbed Epsilon II, debuted in 2008. It is adaptable for front and all-wheel drive applications. In long wheelbase format, Epsilon II supports US EPA Large Cars, allowing GM to replace the G and W platforms. The architecture was developed by Opel in Rüsselsheim, Germany. Many safety features and AWD fitment modifications were done by Saab.^[3]

Current and announced vehicles built on Epsilon II:

• SWB
  • 2008–2017 Opel Insignia, Vauxhall Insignia, Holden Insignia VXR, Buick Regal, Chevrolet Vectra (saloon, hatchback, estate) (SWB)
  • 2012–2016 Chevrolet Malibu, Holden Malibu (SWB)
• SL LWB
  • 2010–2016 Buick LaCrosse/Alpheon (SL LWB)
  • 2010–2012 Saab 9-5 (SL LWB)
  • 2012–2019 Roewe 950 (SL LWB)^[4]
• EL LWB
  • 2012–2019 Cadillac XTS (EL LWB)
  • 2014–2019 Chevrolet Impala (EL LWB)

• Opel Insignia
• Opel Insignia OPC
• Opel Insignia Sports Tourer
• Vauxhall Insignia
• Vauxhall Insignia Estate
• Buick Regal
• Buick Regal GS
• Holden Insignia VXR
• Chevrolet Vectra
• Buick LaCrosse
• Alpheon EL300
• Roewe 950
• Chevrolet Malibu
• Chevrolet Impala
• Cadillac XTS
• Saab 9-5

Concept vehicles built on Epsilon II:

• 2007 Buick Riviera
• 2007 Opel GTC Concept

• Buick Riviera Concept (2007)
• Opel GTC Concept

E2XX is a moderately updated version of Epsilon 2 platform,^[5] consistent with other platform revamps, such as the D2XX based on Delta II.

The E2XX platform targets weight reductions and longer wheelbases.