Most modern plastic model kits are created by using an injection-molding process. The completed kit parts are then glued together with plastic solvent by the end user. Some models can have very detailed decals or paint schematics to make them look as close to the original item the model is made after.
Before computer animated graphics were used, many television shows and even movies used very detailed scale models in the actual movie. Shows like Star Trek and Star Wars made extensive use of detailed scaled models and time lapse motion photography. For that period in history, they produced very exciting visual adventures that took the viewer on a journey all with the use of custom created scale models. Many of the early creations can be bought as kits today.
During the 1950s, the Aurora company became the first to manufacture plastic models and model kits. Shortly after them other manufactures got into the industry and released their own models and kits. In the USA, the most well know model kit manufacturers are probably Revell, AMN and Monogram and in other counties firms like DML and Trumpeter are household names.
Most plastic models are designed to an established scale size. Each model subject has one or more common scales, although they can and do differ from one to the other. The following are the most common scales for popular subjects:
Aircraft: 1/24, 1/32, 1/48, 1/72, 1/100, and 1/144, with 1/48 and 1/72
Military vehicles: 1/35, 1/48 ,1/72, 1/76
Ships: 1/96, 1/350, 1/450, 1/600, 1/700
Railways: 1:43.5 (7 mm/1ft : O scale), 1:76.2 (4 mm/1 ft : OO scale), 1:87 (3.5 mm/1 ft : HO scale)
Today's models do not always conform to their nominal scale size. Many manufactures will slightly alter the scale size to accommodate the packing of the model. This practice has become known as fit-the-box scale.