Today is National Best Friend Day, and we're celebrating by rounding up pictures of our favorite celebrity buddies. Take a look at girlfriends Beyoncé and Gwyneth Paltrow , supportive pals Robert Pattinson  and Katy Perry , and beautiful buds Penélope Cruz and Salma Hayek . There's also Leonardo DiCaprio and his longtime best friend Tobey Maguire , plus so many more. Click through to see them all!
Katy Perry  is close friends with Robert Pattinson , and she reportedly provided him with a shoulder to lean on when he broke up with Kristen Stewart .
Zach Galifianakis  and Bradley Cooper  were friends long before they starred together in The Hangover. Bradley even made an appearance on Zach's short-lived VH1 talk show, Late World, back in 2002 and was one of the first stars to appear on his Funny or Die Between Two Ferns series.
Busy Philipps and Michelle Williams  became buds on the set of Dawson's Creek in the '90s. Busy even set up Michelle with her former boyfriend, Jason Segel .
Being the daughters of famous musicians may explain the bond between Kelly Osbourne and Miley Cyrus . The two have been friends ever since they got close on the set of the straight-to-DVD film So Undercover.
Justin Bieber  used to idolize Usher , and now the singer is one of his closest friends. Usher signed Justin to his record label in 2008 and quickly became the teen's mentor. These days the guys love to perform together and shared the stage at the Billboard Music Awards in 2012.
Taylor Swift  and Emma Stone  met at the Young Hollywood Awards five years ago, and their friendship blossomed from there. Taylor told us in 2011 that Emma is "like a sister to me. She can predict my thoughts."
Drew Barrymore  and Cameron Diaz 's friendship was cemented on the set of the first Charlie's Angels film in 2000. Cameron was a guest at Drew's 2012 wedding .
Lena Dunham and Jemima Kirke have been pals ever since their school days at Brooklyn's St. Ann School. The two have remained very close over the years, with Lena putting Jemima in her film, Tiny Furniture, and her hit TV show, Girls.
Demi Lovato and Selena Gomez 's friendship started more than 10 years ago when they auditioned for Barney together. Demi has said that she's "very lucky to have someone like Selena in my life."
Robert Pattinson  and Tom Sturridge go all the way back to their school days in London. Both guys relocated to the US for their careers around the same time, and they hang out with the same group of British actors in Hollywood.
Kim Kardashian  and La La Vasquez's friendship goes back many years, and the duo still likes to sit front row at fashion shows, watch basketball games, and hit the red carpet together.
Kristen Stewart  counts her Runaways costar Scout Taylor-Compton as one of her close friends. The two met while auditioning for the same roles when they were starting out in Hollywood, but they haven't let the competition keep them from becoming pals.
Funny girls Tina Fey  and Amy Poehler  shared the screen on Saturday Night Live for years, but their friendship actually got started in the '90s while they were both studying improv in Chicago.
Despite past rumors that they were a couple, Eva Longoria  and Mario Lopez are actually more like family. Eva considers Mario a brother, while Mario shows support for his "girl" Eva on Twitter.
Brad Pitt  and George Clooney  put their friendship on the big screen in the Ocean's series. The guys link up regularly for big Hollywood award shows.
David Beckham  and Gordon Ramsay 's friendship goes beyond just guy time; their families are close and even spent Easter together in 2012.
Beyoncé Knowles and Gwyneth Paltrow  have been close friends for years, and frequently double date with their husbands, Jay-Z  and Chris Martin .
Beyoncé told Harper's Bazaar UK of Gwyneth, "She is what I strive to be one day." In the same publication, Gwyneth returned the compliment by calling Beyoncé "the most talented human being on the planet."
They may seem like an odd pairing, but Taylor Swift  and Lena Dunham are close pals. The two forged a friendship after Lena tweeted about liking Taylor's music. Taylor even reportedly hosted Lena at her Rhode Island home for a Memorial Day party.
Leonardo DiCaprio  and Tobey Maguire  have been catching Lakers games together for years, and at the premiere of his film The Details, Tobey talked about working with Leonardo on The Great Gatsby. "The fact that I was forced to see one of my best friends everyday was fantastic."
Nicole Kidman  and Naomi Watts  aren't just fellow Aussie actresses; they're best friends. The ladies were classmates in high school, and their friendship is evident on red carpets to this day. Nicole has said of her friendship with Naomi  that they are "very, very good friends and have maintained that through so many things."
Will Ferrell  and John C. Reilly have never been shy about their relationship. The two have starred in several movies together, including Talladega Nights, and Step Brothers, and at a Lakers game in 2011, they showed some PDA on the kiss cam.
Matt Damon  and Ben Affleck  have been best Boston buds since childhood. They even shared a screenwriting Oscar for Good Will Hunting in 1998. Matt and Ben are still close friends, having enjoyed many vacations with both their families in recent years.
John Krasinski  and Jimmy Kimmel are funny friends and neighbors. They kicked off 2012 together in Hawaii with their significant others and joked about the vacation on Jimmy's talk show.
Pals Katy Perry  and Allison Williams attended the Grammys together last year. Allison said of the date night with Katy , "She's a friend of mine and she's nominated, as she should be. I can't wait to go."
Charlize Theron  and Kristen Stewart  got to know each other while filming Snow White and the Huntsman last year and became fast friends. Charlize told Access Hollywood of Kristen, "I really, I really, really love that girl. I love that girl, like, I would jump off a building for that girl. She's amazing, she's amazing."
Woody Harrelson and Matthew McConaughey  have been longtime friends, and they recently took their relationship to the small screen. Woody and MM were TV costars for the first time in HBO's True Detective, after working together on the big screen in both Edtv and Surfer, Dude.
Justin Bieber  and Jaden Smith are both talented young stars so it should come as no surprise that they both became fast friends. Justin has been supporting Jaden's music career, giving him a highly-coveted spot on his world tour last year.
Salma Hayek  and Penélope Cruz have been pals for years and starred together in 2006's Bandidas.
Reese Witherspoon  met Kate Winslet  in 2007, and they've been buddies since. Reese said of their friendship, "Imagine my good fortune  when Kate Winslet moved into my neighborhood, rang my doorbell, and said, 'Dahling, Sam [Mendes] is off shooting and I believe our children are the same age. Could they possibly have a playdate, and, oh, by the way, it's almost 9 o'clock and I've had nothing to drink — do you have any wine?'"
Rihanna  and Katy Perry  are such good friends that Rihanna  was a part of Katy's small bachelorette party back in 2010. They managed to catch up at Coachella in 2012, and they love to get together whenever their busy schedules allow.
Zac Efron  and Ashley Tisdale  have been buds since their High School Musical days and still spend time together. Ashley even showed her support for Zac at his Lucky One premiere in April 2012.
Lauren Conrad  and Lo Bosworth  have been besties since their time together on Laguna Beach, and their friendship has lasted through their journey to Hollywood.
Jennifer Aniston  and Chelsea Handler have grown close over the last few years and even have taken vacations to Cabo together.
Jennifer presented Chelsea with a Glamour Woman of the Year honor in 2012. At the show, Jen said, "I rarely comment on my personal life. But I'm here to tell you, I'm madly in love. I'm madly in love with the one and only Chelsea Handler."
Leonardo DiCaprio  and Lukas Haas  have been buddies since they first met while auditioning in Hollywood years ago. They stick together for sports games and lavish vacations, and they even attended Coachella together in 2011.
Selena Gomez  and Lily Collins may have both dated Taylor Lautner , but it hasn't stopped the two of them from becoming friends.
Ryan Reynolds  and Sandra Bullock  were introduced by a mutual friend years ago and formed a strong friendship on the set of 2009's The Proposal. They supported each other through divorces, his from Scarlett Johansson  and hers from Jesse James. Ryan's even close with Sandra's little one, Louis.
Sienna Miller  and Channing Tatum  became pals after they met on the set of G.I. Joe: The Rise of Cobra. Sienna even said that she has been giving Channing advice on raising a baby now that he and wife Jenna Dewan are parents.