Kei car, K-car, or keijidōsha (軽自動車^?, lit. "light automobile") (pronounced [keːdʑidoːɕa]), is a Japanese category of small vehicles, including passenger cars, vans, and pickup trucks. They are designed to comply with Japanese government tax and insurance regulations, and in most rural areas are exempted from the requirement to certify that adequate parking is available for the vehicle. This especially advantaged class of cars was developed to promote popular motorization in the post war era. While successful in Japan, the genre is generally too specialized and too small to be profitable in export markets.

The cars feature yellow licence plates, earning them the name "yellow-plate cars" (black numbers on yellow background for private use and yellow numbers on black background for commercial use) in English- and Spanish-speaking circles. Because regulations only restrict physical size and engine displacement (and latterly outright power), manufacturers have been able to introduce many advanced technologies to the class. As a result, kei cars are often available with forced induction engines, automatic and CVT transmissions, front-, rear- and four-wheel drive, hybrid drivetrains, air conditioning, GPS and many other features.

Kei may refer to:

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally for the transport of people rather than goods.

The term motorcar has also been used in the context of electrified rail systems to denote a car which functions as a small locomotive but also provides space for passengers and baggage. These locomotive cars were often used on suburban routes by both interurban and intercity railroad systems.

There are approximately 600 million passenger cars worldwide (roughly one car per eleven people). Around the world, there were about 806 million cars and light trucks on the road in 2007; the engines of these burn over a billion cubic meters (260 billion US gallons) of petrol/gasoline and diesel fuel yearly. The numbers are increasing rapidly, especially in China and India.