The Mattei Affair (Italian: Il Caso Mattei) is a 1972 Italian drama film directed by Francesco Rosi. It depicts the life and mysterious death of Enrico Mattei, an Italian businessman who in the aftermath of World War II managed to avoid the sale of the nascent Italian oil and hydrocarbon industry to US companies and developed them in the Eni, a state-owned oil company which rivaled the "Seven Sisters" for oil and gas deals in Northern African and Middle Eastern countries.

The film shared the Grand Prix with The Working Class Goes to Heaven at the 1972 Cannes Film Festival. Italian star Gian Maria Volonté was the leading actor in both films.

The film is an innovative hybrid of documentary and fiction, representing Francesco Rosi's concept of cine-inchieste (film investigation). The flashback structure shows the influence of Citizen Kane and Rosi's Salvatore Giuliano (1962). Rosi remains faithful to his neo-realist roots with on-location shooting and non-professional actors. The main plot is interwoven with a fictionalized account of the director's own investigation into the death of his friend, the journalist Mauro De Mauro, who disappeared while doing research for the film. He was killed by the Sicilian Mafia, but like the death of Mattei, De Mauro's case was never solved.

In 2008, the film was included among the Italian Ministry of Cultural Heritage’s 100 Italian films to be saved, a list of 100 films that "have changed the collective memory of the country between 1942 and 1978."