Start with what the Renault 18 is: a 4-door sedan (car) / sedan / 5-door station wagon with Petrol engine, built from 1978 to 1994, as the oil crises and the first emissions rules rewired the industry. What it meant takes a little longer.
Where it came from
The Renault 18 is a large family car produced by French manufacturer Renault between 1978 and 1989, with South American production continuing until 1994. It formed the basis for the closely related Renault Fuego Coupé, with which it shared its floorpan and drivetrain, but with the Fuego initially using the negative offset type front suspension from the larger Renault 20/30, which became standardized across the 18 range from the 1983 model year onwards.
Under the skin
The engine is Petrol engine; other versions carried different engines, listed in the specification table below. On the scales it comes to 940 kg. Drive goes through a 4 / 5-speed Manual transmission / manual / 3-speed Automatic transmission / automatic. The layout matters: the engine drives the front wheels, the packaging choice that gives a small car a big cabin. The wheelbase is 2440 mm. These are manufacturer figures carried by Wikipedia and Wikidata, not road-test measurements.
In context
In the Renault line-up the Renault 18 has a clear place: it replaced the Renault 12; it handed the line to the Renault 21 / Eagle Medallion (North America); the factory was Boulogne-Billancourt. The cars a buyer would have weighed it against include the Mazda RX-7, the Toyota Supra, the GM (General Motors) Saab 900. Nearby in the Renault catalogue sit the Renault 10 and the Renault 10CV.
Owning one today
MotorJury scores cars on the United States complaint and recall record, and the Renault 18 has none: too old, too rare, or never sold there. Its value today is a collector's question, decided by provenance and condition rather than by a class average.