With humor and fearless gusto, “This Film Is Not Yet Rated,” the new documentary by Kirby Dick, takes square aim at the surprisingly secretive organization that minds our PG’s and R’s. The Motion Picture Association of America may be best known as moderator of the movie-going public’s intake of sex and violence, but Mr. Dick uncovers an organization rather less savory than its family image.

Lately, the MPAA, in its capacity as powerful industry organization, has done a good enough job of shooting itself in the foot by suing file-sharing students and pimping stuntmen in laughable preshow warnings. “This Film Is Not Yet Rated” initially concerns itself more with the organization’s questionable practices as ratings arbiter than with its business role, but it ultimately shows how the two are inextricable.

The real success of Mr. Dick’s approach lies in objecting not to ratings standards, but to the MPAA’s double standards. He unmasks the willfully mysterious organization’s many unpleasant faces: unaccountable purveyor of insidiously dated sexual attitudes, masterful practitioner of doublespeak, and, most damningly for a supposedly self-regulating industry, distinctly anti-indie shill for studios.

The exposé takes two tacks. First, an engaging lineup of talking heads (including Mary Harron, Kevin Smith, and others from the world of independent film) relate and reflect on their encounters with the infamous ratings board. Kimberley Pierce, whose film “Boys Don’t Cry” won Hilary Swank her first Oscar, recounts the board’s curious insistence on truncating a female character’s orgasmic bliss (“How long is too long?”).

These accounts, backed up by unusual side-by-side comparisons, expose vexing inconsistencies in the treatment of gay and female sexuality. Yes to boy-on-pie action, but no to a girl masturbating fully clothed. Yes to Michael Douglas taking someone aggressively from behind; no to queasy-making gay sex.

America’s dual tendencies toward Puritanism and high body counts are also aired. It’s perhaps a too-familiar conundrum that remains tantalizingly out of the film’s grasp, but it’s fully illustrated in the MPAA’s softer stance on cartoonish violence than even romantically presented sex.

The film’s other, more symbolic strand is the filmmaker’s hunt for the actual identities of the people who comprise the ratings board. Mr. Dick hires an investigator, sweet but persistent, to stake out the MPAA compound and identify the “ordinary folks” whose judgments control the fate of tens of millions of dollars at the box office, not to mention a healthy portion of the popular standards in this country. The entertaining gambit not accidentally pits the director as the sympathetic little guy (for an indie filmmaker, perhaps the only stance available). It fits nicely with today’s do-it-yourself zeitgeist of investigative, bloggish accountability.

The film’s themes come together with Mr. Dick’s ingenious reflexive finale, when he submits his own film for a rating. An ensuing Kafkaesque sequence finds the filmmaker on the phone with the appeals board representative who says board members will not be identified. One moment, the line appears to go dead; then a voice re-emerges: “We’re here. We’re just looking at the rules.”

All this makes for an irresistible story, punctuated by the evil-leprechaun presence of the longtime MPAA chief, Jack Valenti (and some regrettable animations). But this is not a filmmaker interested only in Hollywood hypocrisy. Mr. Dick’s work has been strikingly consistent in examining our society’s fault lines and gray areas, raising complex issues with minimum fuss. His last film, “Twist of Faith,” chronicled the agonizing crisis of faith that struck a Catholic victim of priestly pedophilia. The notorious “Sick” was a portrait of the masochist-artist Bob Flanagan, a sufferer of cystic fibrosis who found control over pain by causing his own.

Those films posed challenging questions about truths we take for granted or we’d rather not mull, and “This Film Is Not Yet Rated” is no different. Is the MPAA reflecting values in its choices, or setting regressive ones in stone? Do standards innocuously described as protecting families amount to political censorship by placing risky subjects off limits? (And is the MPAA even relevant in an age when studios plainly market the uncut versions of their products on DVD?) Artistic freedom, in other words, so frequently batted away as inessential in the battle for American values, is only the tip of the iceberg.

Cynics on different sides may feel Mr. Dick goes too far or not far enough, but economic truths about the industry emerge less controversially. Independent filmmakers seem like second-class citizens in the kingdom of the MPAA. Trey Parker, the co-creator of “South Park” and ever the gleeful giant-killer, reports his divergent experiences when making a small film (“Orgazmo”) and a studio one (the animated “South Park”movie).The MPAA claims to avoid making specific suggestions, lest it be construed as an organ of suppression, yet Mr. Parker received detailed notes on cuts for his big-budget animated comedy (as seems general practice).

Mr. Dick’s final coup is to disclose the names of the MPAA appeals board to whom he took his case. The list shockingly includes several studio distribution executives. The classic conflict of interest, compromising the economic fate of any applicant but especially independents, underlines the organization’s constitutional bias.

Mr. Dick doesn’t mention it, but that’s a nasty little discovery that confronted one of the earliest challengers to the rating system in its infancy in the early 1970s, a young independent filmmaker named Brian De Palma. Then as now, Hollywood faced uncertain economic prospects, and the ratings board was one industry-insulating response for their flagging product. Some things never change, and “This Film” ends, wittily and appropriately, with a song by the 1970s post-punk group Television: “See No Evil.”