From 1939 to 1975, the Franco dictatorship placed Spain in the grip of repressive leadership that, among other abuses of power, exerted strict censorship over the country’s cinema. Following government-mandated restrictions so rigid and ridiculous they made Hollywood’s Hays code look freewheeling in its conservatism, Spanish filmmakers were allowed to make only those films that reflected the values of General Francisco Franco’s fascist Catholic regime — at least for a while.

Then, in the 1960s, when the country’s finances were in trouble, the government turned to movies to save it, partnering with other nations on co-productions in genres — Westerns, horror films, action flicks — that would travel around the globe and put some much-needed cash in Spain’s coffers. That these movies were made in collaboration with Germany, Italy, and other countries gave the Franco regime some plausible deniability when it came to showcasing the sex and violence that had previously been censored — as did the order that none of these films be written to actually take place in Spain, thus allowing the filmmakers to assert they did not reflect Spanish values.

Genres like horror also gave politically oriented filmmakers a way to smuggle subversive ideas past censors, who couldn’t always see that creatures like zombies and werewolves were metaphors meant to critique the established order. As Franco’s dictatorship neared its end, directors became more brazen in their allegories — José Ulloa’s 1974 sci-fi horror film “Creation of the Damned” used its story of a nuclear holocaust as a stand-in for the impending demise of Franco’s regime.

Though national censorship technically remained in place for two years after Franco’s death in 1975, filmmakers began testing the limits of what they could do in terms of sex and violence as well as more radical political commentaries. Just as Alfred Hitchcock took advantage of the Production Code’s weakening position when he made “Psycho” in Hollywood, Spanish filmmakers like Jorge Darnell made films that would have been unthinkable at the height of Franco’s power. Darnell’s 1975 movie “The Devil’s Exorcist,” for example, took on the country’s pervasive Catholicism and, like “The Exorcist” in America, commented on the culture’s widening generation gap.

In 1977, censorship finally ended with the creation of the “S” classification, which was applied to films with extreme content and allowed them to be shown everywhere in Spain, provided no one under 18 years old was admitted. Again, there was a parallel with Hollywood and its creation of the ratings system in 1968; just as that system led to a golden age of personal expression and artistic freedom in the form of movies by Scorsese, Altman, Bogdanovich, Coppola, and many others, the “S” classification yielded a spectacularly diverse group of Spanish movies that attacked the country’s history head-on.

Sex and violence weren’t just sales gimmicks (though they were often that) — they were political acts in and of themselves, responses to decades of religious repression and homophobic and misogynist sentiment. The S-classification era ended in 1983, when a new “X” rating was established for films with extreme sex and violence. X movies were, unlike the S films, restricted. They could only be shown in specialized adult cinemas, thereby ending the creative freedom that had produced so many great genre films. Changes in the way the government subsidized films only made matters worse.

It was great while it lasted, though, and to revisit the Spanish genre films of the 1970s and 1980s is to feel the thrill of an entire country’s liberation. Yet despite these movies’ cultural and historical significance, they’ve been largely inaccessible in the decades since their release, receiving only sporadic home video releases in their home country and virtually no distribution outside it.

This makes Severin’s 10-disc, 19-film Blu-ray boxed set “Exorcismo: Defying a Dictator & Raising Hell in Post-Franco Spain” the first positively essential physical media release this year. Containing new transfers made from the original negatives and over 20 hours of supplementary features, “Exorcismo” provides a crash course in a movement that deserves to be as well-known as Italian Neorealism or the French New Wave.

The set kicks off with Alberto Sedano’s excellent feature-length documentary “Exorcismo: The Transgressive Legacy of Clasificada ‘S,’” which provides a clear and comprehensive overview of the political, economic, and aesthetic factors that intersected to produce the wave of movies represented in the collection. From there, the package moves through an expertly curated selection of movies in chronological order, all representing different aspects of the post-Franco era.

“Creation of the Damned” and “The Devil’s Exorcist” are included, along with important works like León Klimovsky’s “The People Who Own the Dark,” a scathing and haunting horror film that takes class divisions to a provocative and riveting extreme. There are also wild rides like Miguel Madrid’s “Sins of a Nympho,” a movie about a sex party that gives way to philosophical and political discussions; Sedano describes it as “Pasolini on acid in the Spanish Transition,” which gives you some idea of what to expect.

While some of the movies in the “Exorcismo” boxed set examine the country’s past using metaphor and allegory, others — like Manuel Estaba’s 1981 film “Bloody Sex” — explore the trauma of Franco and Spain’s Civil War directly. Still others, like the Spanish-German-Swiss co-production “Triangle of Lust” (directed by Hubert Frank, a Czech filmmaker!), veer more toward exploitation — though even the basest titles in this collection tend to exhibit impressive aesthetic qualities in their cinematography and editing.

There are many more discoveries in “Exorcismo,” and they’re all appointed with superb contextualizing extras in the form of audio commentaries, interviews, and documentaries that dive deep into the histories of each of the films and their makers. There’s also an accompanying book that features must-read liner notes by Sedano (whose efforts to unearth, restore, and promote S-classification films have been beyond heroic), Shelagh Rowan-Legg, and other noteworthy film historians. Taken together, these materials provide a film class in a box that couldn’t be more pleasurable — and, in its demonstration of how clever filmmakers respond to a censorious regime that’s out to silence them, couldn’t be more relevant or useful.

“Exorcismo: Defying a Dictator & Raising Hell in Post-Franco Spain” is now available from Severin.