Maher stated he used a fake title for the film to obtain interviews: "We never, ever, used my name. We never told anybody it was me who was going to do the interviews. We even had a fake title for the film. We called it 'A Spiritual Journey.' It didn't work everywhere. We went to Salt Lake City, but no one would let us film there at all." Creationist Ken Ham of Answers in Genesis, who appeared in the movie, was critical of what he called Maher's "deception" to obtain the interview.
The documentary was produced by Thousand Words and is being distributed by Lionsgate. Originally slated for an international release date coinciding with the Christian Easter holiday 2008 (March 23), post-production delays resulting from a screenwriters guild strike pushed the release date back to July 11, 2008. The movie was released on October 3, 2008.
Religulous had an opening weekend take of $3.5 million from an early October 1 release in LA and NY and also a limited 502 theater release, averaging $6,972 per theater making it #10 in the box office that weekend. Its per-screen receipts were almost three times those of its diametrically opposite rival, the politically conservative An American Carol, which actually edged out Religulous to finish at #9 over the same weekend, but had a per theater average of only $2,325. Only the #1 movie, Beverly Hills Chihuahua, at $9,020, had a higher per-sceen average than "Religulous".
For the second weekend, Religulous had a 35.5% drop in box office receipts and dropped to #13 with a gross of $2,200,000 at 568 theaters for a per screen average of $3,873. 
To date, Religulous has grossed well over $10 million after having a production budget of $2.5 million.
Reviews for Religulous were generally positive, with some mixed and negative reviews. The film received a "Fresh" rating of 70% at Rotten Tomatoes based on 99 reviews, and a "mixed" score of 55 out of 100 at Metacritic based on 29 reviews.Film criticRoger Ebert gave the film a rating of three and a half out of four stars, and wrote: "I report faithfully that I laughed frequently. You may very well hate it, but at least you've been informed. Perhaps you could enjoy the material about other religions, and tune out when yours is being discussed. That's only human nature." Roger Moore of The Orlando Sentinel gave the film a rating of four out of five stars, as did Joe Neumaier of the New York Daily News, who characterized Religulous as "Bill Maher at his best". The film received a rating of three out of four stars from Kyle Smith of the New York Post. Robert W. Butler of The Kansas City Star gave the film a rating of three stars, and commented: "The film is one-sided, less a measured argument than a bunch of rants and barbed observations. But it’s also very funny, which trumps everything else." Owen Gleiberman of Entertainment Weekly gave the film a rating of A-, and wrote: "The movie is funny as...well, hell." Steve Persall of the St. Petersburg Times also gave the film a rating of A-, and commented: "If he offends your particular faith, Maher will soon have you laughing at someone else's, wondering how 'those people' could be so gullible."
The Canadian Press said the movie "delivers a laugh-out loud attack on the most sacred of cows." Christie Lemire, of the Associated Press, wrote: "If you're an atheist or an agnostic, you'll be completely on board and happy to tag along with Maher as he travels the globe asking people about their faith - everywhere from Jerusalem to the Vatican to Amsterdam, where he finds not only the Cannabis Ministry but also a Muslim gay bar (with two people in it)." John Anderson of Newsday wrote: "much that's funny, insightful and thought-provoking. But it certainly doesn't give the religious a lot of slack." Jay Stone of Canwest News Service described the film as "hilarious, sacrilegious and exhausting". Writing for Variety, Robert Koehler wrote that Maher has made a successful transition from a minor comic to a social critic: "Considering he was once a minor comic and a supporting thesp in generally awful film comedies, Maher’s transformation into one of America’s sharpest social critics is remarkable. He takes no script credit, but his periodic monologues to the camera are undeniably written, and written well."
Some reviews have been negative. James Berardinelli wrote, "If the subject of religion is as important to Maher as he claims during his end comments, then he should have followed those words with actions and made a movie that's more than a sum of inauthentic interviews, ranting attacks, and obvious observations. The choir may hum along with Maher but the rest of those watching this movie will be singing the blues." Nick Schager of Slant Magazine called it an "atheistic wannabe-dissection of modern faith" and compared it to Ben Stein's Expelled: No Intelligence Allowed in that he considered both films to have "[employed] a similar, debilitating brand of smug disingenuousness, feigning interest in discussion while arrogantly and speciously preaching in the very same manner that their subjects are ridiculed for". Armond White wrote a critical review of the film in New York Press, and commented: "To scoff at the foundations of charity, justice and love that hold people together, that’s what’s ridiculous." Ben Kenigsberg of Time Out New York gave the film a rating of three out of six stars, and wrote: "The worst scenes in Religulous are appalling for their methods; the best are appalling for their information." Rick McGinnis of Metro gave the film low marks, concluding that "Maher is preaching to the choir with an undisguised dishonesty that only the true believers will forgive."