Prior to 1960, all Chrysler Corp's vehicles were of body-on-frame construction and considered "full-size" (although the brands were progressively larger as they got more expensive).  In 1960, Chrysler adopted uni-body construction for all passenger cars except the Imperial, introduced a compact (Valiant) and downsized the other Plymouths and some Dodges to an intermediate wheelbase length. The result was four distinct "platforms"  that were that coded A-Body (compact), B-Body (midsize), C-Body (fullsize) and Y-Body (Imperials). At the time, these platform designations were only used internally but were handy for the engineering department since it allowed them to communicate about models under development that maybe hadn't been yet named by the marketing department.  These platform designations are now common within the MoPar collector car hobby since cars within a platform will share most of the mechanical components.  For instance, a 1965 Plymouth Fury uses the same battery cable as other 1965 C-Bodies such as a Dodge Polara, Monaco, 880 or as a 1965 Chrysler.

The Imperial soldiered on with its body-on-frame architecture until 1967. From then on, it became more and more like a uni-body and shared progressively more parts with the C-Body Chrysler.  

In 1970, Chrysler Corp.introduced the "E-Body" platform for its Plymouth Barracuda and Dodge Challenger pony cars.

Model names were somtimes shifted from one platform to another as time went on. For example, a 1962 Dodge Dart was a midsize (B-Body) but in 1963, the Dart nameplate was was applied to Dodge's A-Body compact. A 1964 Plymouth Fury is a B-Body but a 1965 or later Fury is a fullsize C-Body. Plymouth's Barracuda was built on the A-Body platform until 1970 at which time the name was used for Plymouth's E-Body offering.