The Jaguar AJ-8 is a compact DOHC V8 piston engine used in many Jaguar vehicles. It was the fourth new engine type in the history of the company. It was an in house design with work beginning before Ford's purchase of the company. In 1997 it replaced both designs previously available on Jaguar cars: the straight-6 Jaguar AJ6 engine, and the Jaguar V12 engine. It remained the only engine type available on Jaguar until 1999 with the launch of the S-Type, when the Jaguar AJ-V6 engine was added to the list. The AJ-V8 is available in displacements ranging from 3.2L to 5.0L, and a supercharged version is also produced. Ford Motor Company also used this engine in other cars, including the Lincoln LS and the 2002–2005 Ford Thunderbird, as well as in several Land Rovers, and the Aston Martin V8 Vantage.

The AJ6, and the similar AJ16, are inline-6 piston engines used by Jaguar cars in the 1980s and 1990s. The AJ6 was designed to replace the successful and long-used Jaguar XK6 engine, and was introduced in 1984. It was only the third all-new engine ever designed by the company. The AJ16 evolution was replaced in 1996 with the Jaguar developed AJ-V8 engine.