structural:summarization, information:extraction
1931–1937: Spain

Spain in the early 1930s was a time of political and social turbulence. Due to both a surge in anti-clerical sentiment and a longrunning desire for retribution for the corruption and malfeasance of the extreme right and their supporters in the church, Anarchists and Radical Socialists sacked monarchist headquarters in Madrid and proceeded to burn down or otherwise wreck more than a dozen churches in the capital. Similar revolutionary acts occurred in many other cities in southern and eastern Spain, in most cases with the acquiescence and occasionally with the assistance of the official Republican authorities.

Buñuel's future wife, Jeanne Rucar, recalled that during that period, "he got very excited about politics and the ideas that were everywhere in pre-Civil War Spain". In the first flush of his enthusiasm, Buñuel joined the Communist Party of Spain (PCE) in 1931, though later in life he denied becoming a Communist.

In 1932, Buñuel was invited to serve as film documentarian for the celebrated Mission Dakar-Djibouti, the first large-scale French anthropological field expedition, which, led by Marcel Griaule, unearthed some 3,500 African artifacts for the new Musée de l'Homme. Although he declined, the project piqued his interest in ethnography. After reading the academic study, Las Jurdes: étude de géographie humaine (1927) by Maurice Legendre, he decided to make a film focused on peasant life in Las Hurdes, perhaps the poorest comarca in Extremadura, one of Spain's poorest regions. The film, called Las Hurdes: Tierra Sin Pan (1933), was financed on a budget of 20,000 pesetas donated by a working-class anarchist friend named Ramón Acín, who had won the money in a lottery. In the film, Buñuel matches scenes of deplorable social conditions with narration that resembles travelogue commentary delivered by a detached-sounding announcer, while the soundtrack thunders inappropriate music by Brahms.

"Though the material is organized with masterly skill, the very conception of 'art' here seems irrelevant. It is the most profoundly disturbing film I have ever seen."

Award-winning film director Tony Richardson on Las Hurdes: Tierra Sin Pan

Las Hurdes was banned by the Second Spanish Republic and then by the Francoist dictatorship. It is a film which continues to perplex viewers and resists easy categorization by film historians. Las Hurdes has been called one of the first examples of mockumentary, and has been labeled a "surrealist documentary", a term defined by critic Mercè Ibarz as "A multi-layered and unnerving use of sound, the juxtaposition of narrative forms already learnt from the written press, travelogues and new pedagogic methods, as well as a subversive use of photographed and filmed documents understood as a basis for contemporary propaganda for the masses". Catherine Russell has stated that in Las Hurdes, Buñuel was able to reconcile his political philosophy with his surrealist aesthetic, with surrealism becoming "a means of awakening a marxist materialism in danger of becoming a stale orthodoxy".

After Las Hurdes in 1933, Buñuel worked in Paris in the dubbing department of Paramount Pictures, but following his marriage in 1934, he switched to Warner Brothers because they operated dubbing studios in Madrid. A friend, Ricardo Urgoiti, who owned the commercial film company Filmófono, invited Buñuel to produce films for a mass audience. He accepted the offer, viewing it as an "experiment" as he knew the film industry in Spain was still far behind the technical level of Hollywood or Paris. According to film historian Manuel Rotellar 's interviews with members of the cast and crew of the Filmófono studios, Buñuel's only condition was that his involvement with these pictures be completely anonymous, apparently for fear of damaging his reputation as a surrealist. Rotellar insists, however, "the truth is that it was Luis Buñuel who directed the Filmófono productions". José Luis Sáenz de Heredia, the titular director of two of the films created during Buñuel's years as "executive producer" at Filmófono, recounted that it was Buñuel who "explained to me every morning what he wanted...We looked at the takes together and it was Buñuel who chose the shots, and in editing, I wasn't even allowed to be present." Of the 18 films produced by Buñuel during his years at Filmófono, the four that are believed by critical consensus to have been directed by him are:

During the Spanish Civil War (1936–1939), Buñuel placed himself at the disposal of the Republican government. The minister for foreign affairs sent him first to Geneva (September 1936) and then to Paris for two years (1936–38), with official responsibility for cataloging Republican propaganda films. Besides the cataloguing, Buñuel took left-wing tracts to Spain, did some occasional spying, acted as a bodyguard, and supervised the making of a documentary, entitled España 1936 in France and España leal, ¡en armas! in Spain, that covered the elections, the parades, the riots, and the war. In August 1936, Federico García Lorca was shot and killed by Nationalist militia. According to his son, Juan Luis, Buñuel rarely talked about Lorca but mourned the poet's untimely death throughout his life.

Buñuel essentially functioned as the coordinator of film propaganda for the Republic, which meant that he was in a position to examine all film shot in the country and decide what sequences could be developed and distributed abroad. The Spanish Ambassador suggested that Buñuel revisit Hollywood where he could give technical advice on films being made there about the Spanish Civil War, so in 1938, he and his family traveled to the United States using funds obtained from his old patrons, the Noailles. Almost immediately upon his arrival in America, however, the war ended and the Motion Picture Producers and Distributors Association of America discontinued making films on the Spanish conflict. According to Buñuel's wife, returning to Spain was impossible since the Fascists had seized power, so Buñuel decided to stay in the U.S. indefinitely, stating that he was "immensely attracted by the American naturalness and sociability".