The Van's RV-4 is a light homebuilt aircraft supplied in kit form. It seats two people in a tandem seating configuration with the pilot accommodated in the front seat.

The Van's RV series has become the most popular kit-built aircraft in the world. The RV-4 is the second most popular RV model, outsold only by the now discontinued RV-6.

As of February 2010, 1309 RV-4s had been completed and flown worldwide.

Richard VanGrunsven designed the RV-4 in the mid 1970s as a two-seat development of the single-seat RV-3. The RV-4 prototype first flew in August 1979.

The RV-4 is a new design based upon the concepts proven in the RV-3 and is not merely a stretched RV-3. The RV-4 airframe will accept a range of engines up to 180 hp (134 kW), including the Lycoming O-360. The RV-4 has a new wing, with increased wingspan and wing area over the RV-3. The RV-4 is designed for sport aerobatics.

The RV-4 has proven to be a capable cross country aircraft in service, able to carry two modest sized people and baggage on longer trips. RV-4s have been flown around the world, notably by an Australian, Jon Johanson, who completed world-girdling RV-4 flights on two occasions.

Many larger people find the RV-4 cockpit design physically constraining, and as a result VanGrunsven has designed an entire family of derivative designs. The RV-6 was designed to allow side-by-side seating, and the RV-8 was created as an enlarged aircraft that follows the RV-4's philosophy and offers tandem seating in a bigger aircraft.

Unlike most later RV series designs, RV-4 kits are only available with conventional landing gear, although some may have been constructed in tricycle configuration by builders. At least two RV-4s have also been built with retractable landing gear (mostly for the engineering challenge, as the performance gains were modest).