Kei cars, K-cars, or keijidōsha (軽自動車, lit. "light automobile") (pronounced /keːdʑidoːɕa/), are a Japanese category of small vehicles, including passenger cars, vans, and pickup trucks. They are designed to exploit local tax and insurance regulations, and in most rural areas are exempted from the requirement to certify that adequate parking is available for the vehicle. These standards originated in the times following the end of the Second World War, when most Japanese could not afford a full-sized car yet had enough to buy a motorcycle. To promote the growth of the car industry, as well as to offer an alternative delivery method to small business and shop owners, kei car standards were created.

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, engine displacement and power, manufacturers have introduced 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.

Daihatsu, Honda, Mitsubishi, Smart, Subaru, and Suzuki all manufacture kei cars, while Nissan sells badge-engineered Mitsubishi and Suzuki models, and Mazda offers badge-engineered Suzuki models.