Hollywood’s summer movie season used to begin on Memorial Day weekend. This year, it’s well under way, with two bona fide blockbusters getting an early jump on the competition: “Fast Five” (which opened April 29) and “Thor” (May 6).

The competition promises to be stiff, with more than 50 films slated for release between now and the end of August. Mark your calendars — but do so in pencil, as opening dates are subject to change.

Not surprisingly, given this week’s opening of a fourth “Pirates of the Caribbean” film, there’s no shortage of sequels in store. The animated ones are aimed at the smaller kids: “Kung Fu Panda 2” (May 26), “Winnie the Pooh” (July 15) and a 3-D “Cars 2” (June 24). Two others target teens and young adults with a lot of high-tech special effects: “Spy Kids 4: All the Time in the World” (Aug. 19) and a 3-D “Transformers: Dark of the Moon” (July 1).

Horror fans may relish the prospect of “Final Destination 5” (Aug. 12). More serious-minded and thought-provoking is “Rise of the Planet of the Apes” (Aug. 5), which revives the franchise with state-of-the-art computer-generated primates — plus James Franco as a genetic scientist. Less serious-minded and thought-provoking is the buddy comedy “The Hangover, Part II” (May 26), which moves the action from Vegas to Thailand.

Most likely to succeed in appealing to audiences across the board: “Harry Potter and the Deathly Hallows, Part 2” (July 15), which ends the phenomenal series and bids farewell to its beloved cast of characters with a 3-D flourish.

“X-Men: First Class” (June 3) is officially a prequel to the trilogy of earlier “X-Men” films, with James McAvoy, Michael Fassbender and Jennifer Lawrence as younger versions of Professor Xavier, Magneto and Mystique. It’s also one of several additions this summer to the ever-growing crop of movies about comic book superheroes. Among the others: Ryan Reynolds as “Green Lantern” (June 17) and Chris Evans as “Captain America: The First Avenger” (July 22), both in 3-D.

Partly an archetypal Western and partly a sci-fi thriller, the action-packed “Cowboys & Aliens” (July 29), co-starring Daniel Craig and Harrison Ford, derives from a graphic novel and isn’t in 3-D. “Conan the Barbarian” (Aug. 19), a remake of the 1982 Arnold Schwarzenegger vehicle, originated as a pulp-magazine serial and is in 3-D. Part live action, part animation and based on a TV cartoon, even “The Smurfs” (Aug. 3) gets in on the 3-D craze.

“Fright Night” (Aug. 19), a remake of a 1985 cult favorite, casts Colin Farrell as a vampire. Katie Holmes headlines the haunted-house chiller “Don’t Be Afraid of the Dark” (Aug. 26), a remake of a 1973 TV movie. Comparatively speaking, the scary notion of an alien invasion in writer-director J.J. Abrams’ “Super 8” (June 10) sounds downright original.

Elsewhere, romance is in the air for Anne Hathaway and Jim Sturgess in “One Day” (Aug. 19), Justin Timberlake and Mila Kunis in “Friends With Benefits” (July 22), Rachel McAdams and Owen Wilson in Woody Allen’s “Midnight in Paris” (June 10), Ewan McGregor and Melanie Laurent in “Beginners” (June 3), Emma Roberts and Freddie Highmore in “The Art of Getting By” (June 17) and for Steve Carell, Julianne Moore, Ryan Gosling and Marisa Tomei in “Crazy Stupid Love” (July 29).

Crazy (if not stupid) comedies on tap include Cameron Diaz portraying the rowdy, irreverent, foul-mouthed title character in “Bad Teacher” (June 24) and Jennifer Aniston, Colin Farrell and Kevin Spacey as “Horrible Bosses” (July 8), opposite Jason Bateman and Jason Sudeikis as put-upon underlings bent on revenge. “The Change-Up” (Aug. 5) also features Bateman with Ryan Reynolds as boyhood friends who switch bodies. Paul Rudd plays “Our Idiot Brother” (Aug. 26) to sisters Elizabeth Banks, Zooey Deschanel and Emily Mortimer.

Jim Carrey is a cold-hearted real estate tycoon who warms up to six adorable feathered friends in the family film “Mr. Popper’s Penguins” (June 17). Kevin James talks to the animals in “Zookeeper” (July 8) — and they talk back (in the voices of Cher, Nick Nolte, Adam Sandler and Sylvester Stallone). A pet cat narrates director Miranda July’s “The Future” (July 22).

For laughs involving a criminal element, an unconventional Irish cop (Brendan Gleeson) and a by-the-book FBI agent (Don Cheadle) make unlikely partners in “The Guard” (Aug. 19). In “30 Minutes or Less” (Aug. 12), Jesse Eisenberg is a pizza delivery guy kidnapped and forced to rob a bank.

Billed as a “dramatic comedy,” “Larry Crowne” (July 1) features Tom Hanks (who also wrote and directed the film) as a suddenly unemployed businessman who heads back to college — where he falls for Julia Roberts as one of his professors. Vera Farmiga also stars in her directorial debut, “Higher Ground” (Aug. 26), a drama set in the 1960s feminist movement.

Other more serious alternatives this summer: white debutante Emma Stone and black maid Viola Davis experience the ’60s civil rights movement in “The Help” (Aug. 12); Terrence Malick’s “The Tree of Life” (June 3) alternates between the 1950s and the present to tell the “impressionistic” story of a father (Brad Pitt) and his grown son (Sean Penn); Wayne Wang directs the multi-generational Chinese saga “Snow Flower and the Secret Fan” (July 15); Kristin Scott Thomas plays an American journalist in France in “Sarah’s Key” (July 22); and Robert Duvall is a reclusive old rancher who fosters an aspiring young golfer (Lucas Black) in “Seven Days in Utopia” (Aug. 12).