The Mitsubishi Sigma was the name given to several vehicles manufactured by Mitsubishi Motors between 1976 and 1996 For the sedan built between 1976 and 1987 and known as the Mitsubishi Galant S (Sigma) The Mitsubishi Galant is an automobile manufactured by Mitsubishi Motors since 1969. The name was derived from the French galant, meaning "chivalrous". There have been nine distinct generations, and cumulative sales now exceed five million.

It began as a compact sedan, but over the course of its life has evolved into a larger mid-size car. Initial production was based only in Japan, but since 1994 the American market has been served by vehicles assembled at the former Diamond-Star Motors (DSM) facility in Normal, Illinois. For the third and fourth generations of the Mitsubishi Galant built and sold locally in Australia from 1977 to 1987, The Chrysler Sigma was a version of the Mitsubishi Galant automobile built by Chrysler's Australian manufacturing facility in Adelaide from 1977. When Mitsubishi Motors took over the manufacturing facility in 1980, they renamed the vehicle the Mitsubishi Sigma. The range was discontinued in 1987, and replaced by the Mitsubishi Magna. For the export versions of the Mitsubishi Diamante sedan and station wagon from 1990 to 1996, The Mitsubishi Diamante was first introduced to the public at the Tokyo Motor Show in 1989, and went on sale in Japan in May 1990. It became the second generation Magna, replacing the widened 1983 Galant Sigma manufactured and sold in Australia as a Mitsubishi Verada (the 1987 Galant was downsized, thus leaving a gap in the product range for the Diamante). There have been rumors that the Diamante was either not intended for a Japanese launch, or it might have been planned as a low-volume model. The reason for this argument is that until 1989, the width of vehicles was a vital indication of taxation class. The Diamante, being wider than the 1700 mm break, would have suffered a large tax penalty against most of its rivals, which were designed to be just under limit. At the time, Mitsubishi's image was also considered less than ideal for the marketing of a luxury car—its most expensive offering that the time, the Debonair, was largely seen as a company car project for Mitsubishi conglomerate executives. However, the tax situation had changed in 1989, and the Diamante became the surprise hit of 1990. Amidst Japan's bubble economy, many private car owners sought an executive car in a market that had very few new offerings that year.