A kit car, also known as a "component car", is an automobile that is available as a set of parts that a manufacturer sells and the buyer then either assembles into a car themselves, or retains a third party to do part or all of the work on their behalf. Usually, many of the major mechanical systems such as the engine and transmission are sourced from donor vehicles or purchased from other vendors new. Kits vary in completeness ranging from as little as a book of plans to a complete set with all components included.