Mobile Suit Gundam debuted in 1979 and the first Gunpla kits came in 1980, following the show's cancellation. Parts came in up to 3 different colored sprues. They lacked articulation and detail and required glue and paint to build and finish.
Following the completion of the TV series line, Bandai introduced the MSV (Mobile Suit Variation) line, featuring alternate variants of the series' mobile suits. One of the highlights of the line was the RX-78 Perfect Gundam, which introduced System Injection (a process where one sprue -sometimes even one part - was molded in multiple colors), which minimized the need to paint the model.
Following a line of kits from the Round Vernian Vifam series, the 1985 Mobile Suit Zeta Gundam kit line incorporated the use of polycaps (soft plastic, typically Polyethylene) as connectors for better articulation of joints. The 1987 Gundam Sentinel model line introduced the concept of snap-fit models, reducing the need to use glue. And starting from the 1988 Mobile Suit Gundam: Char's Counterattack line, all Gunpla kits feature snap-fit assembly.
In 1990, Bandai introduced the High Grade (HG) line, which featured newer 1:144 scale versions the RX-78-2 Gundam, the RX-178 Gundam Mk. II, the MSZ-006 Zeta Gundam and the MSZ-010 ZZ Gundam. Each kit boasted exceptional detail and articulation, as well as features normally found in their larger-scale versions such as the Gundam's Core Block System and the Zeta's transformation feature.
Beginning with Mobile Suit Victory Gundam in 1993, a unified set of polycap joints was created for smaller scale models that allowed easy mass production of models that all shared the same basic skeletal frame. This standardization allowed Bandai to release more models over a shorter period. As a result, the Gundam shows of the '90s usually received sizable 1:144 model lines. These were all of similar quality, with some attention to colors molded in the right area, a reasonable level of detail for their price point, and mobility as such that all major joints had at least some degree of mobility.
In 1995, the 1:100 Master Grade (MG) line was introduced. This line features more parts, better detail and improved articulation than past kits of the same scale. As of 2011, the MG line features the most sophisticated 1:100 Gundam model kits produced by Bandai.
Following the release of the Perfect Grade Evangelion, Bandai introduced the 1:60 Perfect Grade (PG) line to the Gundam series in 1998. This line features extensive detail and articulation, as well as working skeletal systems and light-up features. The PG line is the most expensive among all Gunpla kits, and only a select few mobile suits have been released in this line.
To celebrate the 20th anniversary of the franchise in 1999, Bandai released 1:144 First Grade (FG) kits of mobile suits from the original series. Marketed as budget models, these snap-fit kits featured the simplicity of the original kits, but with more modern designs based upon the corresponding Perfect Grade kits.
Mobile Suit Gundam SEED introduced a new type of a non-graded (NG) model, with a completely different design plan. While these still feature snap-fit and color molding, they omit major joints, opting instead to only allow critical pieces to move - typically the neck, hips, shoulders, and feet. These are budget models, usually retailing much lower than other models; and this line was extensive, covering nearly every machine to be featured in the TV series. Gundam SEED also featured non graded 1:100 models, identical in quality to Bandai's High Grade offerings.
In 2010, Bandai released the 1:48 Mega Size Model RX-78-2 Gundam kit as part of the franchise's 30th anniversary campaign. This kit features many innovations that make it easy to assemble for first-time Gunpla collectors. For example, the parts are attached to sprue gates thin enough to break without the need to use of plastic cutters, and excess gate plastic can be removed from the parts without using a hobby knife. Some sprues have been designed to snap together for easy and quick removal of assembled parts. Also in the same year, Bandai introduced the 1:144 Real Grade (RG) line, which takes design elements from the MG line such as an inner skeletal frame.
In 2011, Bandai released the Entry Grade (EG) line, a low-cost model series that replaces the 1:144 NG and FG lines. Unlike other kits of the same scale, all EG kits are made in China.