Four thirds system
The Four Thirds system was created to standardize a new generation of digital cameras. Sigma Corporation as well as several other companies are participating in this system.
This new standard will define the lens mount size, distance from the image sensor and lens-camera communication. The sensor size and aspect ratio (18×13.4mm / 4:3) will also be standardized.
Four Thirds Cameras
Olympus : E-300, E-330, E-1, E-400, E-410, E-500, E-510
Panasonic: Lumix DMC-L1
Leica: Digilux 3
Sigma Four Thirds Lenses
105mm f2.8 EX DG Macro
150mm f2.8 EX DG Macro
18-50mm f3.5-5.6 DC
18-50mm f2.8 EX DC Macro
55-200mm f4-5.6 DC
135-400mm f4.5-5.6 (discontinued)
50-500mm f4-6.3 EX DG
For more info on the Four Thirds system: http://www.four-thirds.org/en/