The Four Thirds System is a standard created by Olympus and Eastman Kodak for digital single-lens reflex camera (DSLR) design and development. Four Thirds refers to both the size of the image sensor (4/3") as well as the aspect ratio (4:3). The Olympus E-1 was the first Four Thirds DSLR, announced and released in 2003. In 2008, Olympus and Panasonic began publicizing the Micro Four Thirds system, a mirrorless camera system which used the same sensor size; by eliminating the reflex mirror, the Micro Four Thirds cameras were significantly smaller than the Four Thirds cameras. The first Micro Four Thirds cameras were released in 2009 and the final Four Thirds cameras were released in 2010; by that time, approximately 15 Four Thirds camera models had been released by Olympus and Panasonic in total. The Four Thirds system was quietly discontinued in 2017, six years after the final cameras were released.

Olympus Corporation is a Japanese manufacturer of optics and reprography products. Olympus was established on 12 October 1919, initially specializing in microscopes and thermometers. Olympus holds roughly a 70 percent share of the global endoscope market, estimated to be worth approximately US$2.5 billion. Its global headquarters are located in Hachioji, Tokyo, Japan.