Lancia's traditional design partner was Pininfarina, but Bertone sought to create a relationship with the manufacturer. Chief designer Marcello Gandini — already known for the Lamborghini Miura and working concurrently on the Countach — used the running gear of a Fulvia Coupé owned by a friend to build a functioning concept, which Bertone personally drove to the Lancia factory gates in a dramatic pitch. The stunt worked, and Lancia agreed to develop a new purpose-built rally car.
Lancia presented the Bertone-designed Stratos HF prototype at the 1971 Turin Motor Show. The car's most distinctive visual element was a crescent-shaped wrap-around windshield providing maximum forward visibility, a striking contrast to its almost non-existent rear visibility. The prototype passed through three engine configurations during development — a Lancia Fulvia unit, a Lancia Beta engine, and finally the mid-mounted Dino Ferrari V6 that would power the production car. Securing that engine required negotiations with Enzo Ferrari, who was initially reluctant to supply a unit to what he viewed as a competitor to his own Dino V6; he relented after the Dino model ended production, ultimately delivering 500 engines to Lancia.
The final design shares certain visual signatures with Gandini's Lamborghini Miura — dual clamshell hoods, curved door-glass lines — but the Stratos received its own identity through an extremely short, wide wedge form so aggressive the nose drops below the top crests of the front wheels.
Lancia undertook extensive testing in 1972 and 1973 to prepare the Stratos for Group 4 homologation, which required production of 500 road cars. Production commenced in 1973 and was completed in 1975. The road-going Stratos HF Stradale was powered by the Dino 2.4-litre V6 producing 190 PS at 7,000 rpm and 226 Nm of torque, giving a 0–100 km/h time of 6.8 seconds and a top speed of 232 km/h. The car weighed between 900 and 950 kilograms depending on configuration.
Competition versions produced approximately 275 hp in original 12-valve specification, rising to around 320 hp with 24-valve heads. From the 1978 season the 24-valve configuration was banned from Group 4 competition by a rule change requiring re-homologation, but even in reduced-power form the Stratos remained highly competitive.
The three leading figures behind the Stratos rally programme were Lancia team manager Cesare Fiorio, British engineer and racer Mike Parkes, and factory driver Sandro Munari. Calculations on chassis, steering, suspension, and engine components were handled by Nicola Materazzi.
The Stratos was homologated for the 1974 WRC season and won the manufacturers championship in that year and the two that followed, with drivers including Sandro Munari and Björn Waldegård. Munari took victories at the 1975, 1976, and 1977 Monte Carlo Rally. The car also won the 1974 Targa Florio, the Tour de France Automobile five times between 1973 and 1980, and the Giro d'Italia automobilistico in 1974, 1976, and 1978.
The Stratos's factory WRC programme was curtailed by internal Fiat Group politics that redirected rallying resources toward the Fiat 131 Abarth. Without works support, the Stratos continued to win in the hands of experienced private teams. Bernard Darniche took the car's final WRC victory at the 1981 Tour de Corse, seven years after the model's homologation.
Lancia also built two Group 5 turbocharged silhouette-class Stratos cars for closed-circuit endurance racing. These were engineered by Nicola Materazzi but proved unable to match the Porsche 935 on pure circuit work, though they found success in hybrid road-and-circuit events. One car was destroyed in a fire at Zeltweg. The other was eventually shipped to Japan for the Formula Silhouette series before passing through several collectors' hands, including Austrian collector Ernst Hrabalek.
In the 1976 24 Hours of Le Mans, a Stratos driven by Christine Dacremont and Lella Lombardi finished 20th overall and second in the GTP class.
A unique Group 5 Stratos was campaigned in European Rallycross by Austrian driver Andy Bentza and, before him, Franz Wurz — father of Formula One driver Alexander Wurz. In 1976 Franz Wurz claimed the first FIA-recognised European Rallycross Championship title with the car. The Stratos was later fully restored and revealed at a public event in May 2016 in its original Memphis livery, converted back to its 1976 rallycross specification.
The Lancia Stratos HF was the first rally car designed from scratch for the discipline rather than adapted from a road car, and its dominant three-year WRC championship run established Lancia's credentials as a serious motorsport constructor. Its combination of Gandini's iconic bodywork, Ferrari-sourced power, and race-winning engineering has made it one of the most recognisable and admired competition cars ever built.