The Ferrari Berlinetta Boxer (BB) is a series of sports cars produced by Ferrari in Italy between 1973 and 1984. The BB was designed by Leonardo Fioravanti at Pininfarina. The first BB model, the 365 GT4 BB, replaced the front engined Daytona and was the first in a series of road-going Ferraris equipped with a mid-mounted flat-twelve engine. The 365 GT4 BB was succeeded in 1976 by the BB 512, equipped with a larger displacement engine, then by the fuel-injected BB 512i in 1981. The series was discontinued in 1984 when the BB 512i was replaced by the Testarossa, which used a revised version of the flat-twelve engine.

Production of the BB was a major step for Enzo Ferrari. He felt that a mid-engined road car would be too difficult for his buyers to handle, and it took many years for his engineers to convince him to adopt the layout. This attitude began to change as the marque lost its racing dominance in the late 1950s to mid-engined competitors. As a result, the rear-mid-engined 246 P Formula 1 car was introduced in 1960, followed by the Dino SP racing sports prototypes in 1961. In 1963, the company also moved its V12 engines to the rear with its P and LM racing cars.

Introduced in 1967, the Dino 206 GT and 246 GT/GTS road cars were the first road-going Ferraris to use the rear-mid-engined layout, albeit under the lower-cost Dino marque. Ferrari's flagship V12-powered road cars remained front-engined through the early 1970s, with the 365 GTB/4 Daytona and 365 GTC/4 introduced in 1968 and 1971, respectively. In 1973, Ferrari introduced the 365 GT4 Berlinetta Boxer as its first mid-engined 12-cylinder road car.

Ferrari first used the flat-12 engine layout in racing cars, starting with the 1964 512 F1. The 512 F1's 1.5 liter engine was designed by Mauro Forghieri, technical director of the racing department. This engine design was further developed in several Formula One and sports prototype racing cars, including the 1968 212 E, 1970-75 312B, and 1971 312PB. These racing engine designs became the basis for the road-going flat 12 engine introduced in the 365 GT4 BB.

Following the introduction of the production 365 GTB/4 Daytona in 1969, Ferrari engineers led by Dr. Ing. Angelo Bellei began work on a successor, the 365 GT4 BB. Though it shared its numerical designation with the 365 GTB/4 Daytona, the 365 GT4 BB was radically different in layout than the front-engined 365 GTB/4. The new car was to have rear mid-mounted flat-12 engine, arranged longitudinally. While this configuration was unprecedented among Ferrari road cars, the design team drew upon the existing chassis design of the mid-engine 250 LM and Dino 206/246, as well as the flat-12 engines developed for the Scuderia Ferrari beginning in 1964. The first prototype 365 GT4 BB was unveiled at the 1971 Turin Motor Show. Prototypes were further refined by an extensive road and track testing program led by Ferrari test driver Giorgio Enrico. As Ferrari engineers already had considerable experience with both the layout and engine design, development work proceeded rapidly and only small changes were seen between the early prototypes and the first production 365 GT4 BB. The production 365 GT4 BB was first offered for sale in 1973.

Dr. Ing. Giuliano de Angelis oversaw the development of the Tipo F102A engine used in the 365 GT4 BB. This engine was derived from both the Mauro Forghieri-designed Tipo 001 3.0-litre flat-12 engine used in the 1969 Ferrari 312B Formula One car and the roadgoing 365 GTB/4 engine. The total displacement of the new engine was 4390.35 cc with a bore of 81 mm and a stroke of 71 mm, dimensions which matched the 365 GTB/4 engine.

While the "Berlinetta Boxer" name has been used by both Ferrari and the press to describe BB-series cars, this engine was not a true boxer engine. In the Tipo F102 A and its derivatives, each pair of opposing pistons share the same crank pin and move in the same direction during operation. In a boxer engine, pairs of opposing pistons move in opposite directions. On this point, Ferrari engine designer Mauro Forghieri stated "Please, don't call it boxer. Technically, it is correct to say that this engine is a flat-12, or has 12 cylinders with the heads at a vee angle of 180°."

The engine block was constructed of Silumin alloy, with cast iron cylinder liners. Pistons were light alloy and the crankshaft was forged steel. The cylinder head design was very similar to that of the 365 GTB/4, incorporating dual overhead camshafts and two valves per cylinder. The four camshafts were driven by two timing belts, which reduced noise and weight compared to the timing chains used on earlier 12 cylinder Ferrari engines. Air and fuel were supplied via four 3-bbl Weber 40 IF 3C carburetors. The ignition system consisted of a single Magneti Marelli distributor and two coils. The engine was lubricated by a wet sump, which was replaced by a dry sump in the BB512 to avoid oil starvation issues. According to de Angelis and Bellei, the first prototype F102 A engine produced 380 bhp at 7,100 rpm and propelled the prototype to 302 km/h (188 mph) during testing. Ferrari brochures reported the production version of the F102 A engine produced 360 bhp at 7,500 rpm and 311 ft/lb of torque at 4,500 rpm, although figures reported in other factory and press publications vary.