We all know The Big Lebowski has a huge cult following, but it's not like it spawned a religion or anything, right?

Wrong.

Dudeism

Believe it or not, a religion devoted entirely to spreading the teachings of The Dude was founded in 2005. Called Dudeism and described by its creators as "the slowest-growing religion in the world," Dudeism "preaches non-preachiness, practices as little as possible, and above all, uh … lost my train of thought there." Also referred to as The Church of the Latter-Day Dude, the organization has ordained over 270,000 Dudeist priests around the world. They celebrate holidays by taking naps and … wait, what?

Lebowski Fest

Really devoted fans of the film call themselves "achievers." In 2002, a group of achievers set up a Lebowski Fest in Louisville, Kentucky, that attracted 150 fans. In the years since, attendance has grown exponentially, and Lebowski Fest has expanded to several other cities.

Lebowski Fest activities typically include a night of unlimited bowling, costume and trivia contests, and a competition to see who's traveled the farthest. At the 2011 Lebowski Fest in New York, Jeff Bridges, John Goodman, Julianne Moore, Steve Buscemi, and John Turturro all reunited to reminisce about the whimsical months they spent making The Big Lebowski. And to answer annoying questions from superfans.

What's a Cult Film, Anyway? A Quick Digression

Lots of popular, outsider-type movies are called cult films, but what makes a cult film other than intensely devoted fans? Genius semiotics prof. Umberto Eco had this to say about it:

What are the requirements for transforming a book or movie into a cult object? The work must be loved, obviously, but this is not enough. It must provide a completely furnished world so that its fans can quote characters and episodes as if they were aspects of the fan's private sectarian world, a world about which one can make up quizzes and play trivia games so that the adepts of the sect recognize through each other a shared expertise. […] Only an unhinged movie survives as a disconnected series of images, of peaks, of visual icebergs. It should display not one central idea but many. It should not reveal a coherent philosophy of composition. It must live on, and because of, its glorious ricketiness. (Source)

He could have been describing The Big Lebowski, but he was actually writing about Casablanca.

As a New York Times reviewer went on to comment:

If the phrases "Nice marmot," or "You're entering a world of pain," or "I can get you a toe" mean anything to you, then "Lebowski" has entered your private sectarian world. (Source)

Conclusion: definitely cult.