The Shelby Mustang was produced from 1965 to 1970 by Carol Shelby in large part due to the great success Ford had with the Mustangs.  The sporty looking Ford Mustang of 1964 lacked high-end performance so Ford decided ask Carol Shelby for help.  By 1965, Shelby had established a factory in Los Angeles, California producing a couple of hundred GT350s a month.

The GT 350, the first Shelby Mustangs, used GT in the name to designate that the car was based on the Mustang GT (Grand Tourism). The reason for the 350 designation is not clear but believed to have been chosen because it was larger than any other number that was on a car badge at the time and because it was a fairly rounded number.  Some cars were then given a suffix such as the "R" (GT 350R) which stands for "racing", and the "H" (GT 350H) which stand for "Hertz" and these cars were manufactured for the Hertz car company. 

By 1967, performance car enthusiasts were looking for big engine in a small car and Shelby responded with a GT500.  The GT500 featured a 428 cubic inch engine in a modified Mustang chassis.  The GT500 badge was used to identify a Shelby Mustang with a big block engine to allow it to be distinguished from it's small block stable mate. 

Over time, the GT350 was enlarged to 302 and 351 cubic inches and the factory was relocated to Michigan.  The 428 engines were also replaced by a Cobra Jet 428 in Shelby's pursuit to ever increasing performance.  The Shelby Mustang was manufactured in fastbacks, convertibles and coupes.  The majority of Shelby Mustangs were fastbacks with fewer convertibles and very few coupes.

By 1969, Ford Motor Company was competing with itself by supporting the Shelby Mustang project and preparing to build Boss 302 and Boss 429 Mustangs in their own plants. This combined with increased safety regulations lead to the end of the Shelby Mustang era.  Production of the Shelby Mustangs was supposed to end in 1969 but a few left over 1969 cars resulted in a few Shelby Mustangs being released in 1970.