Every once in a while, our favorite starlets like to show a little extra affection for each other. Sometimes these kisses are innocent pecks on the cheek, while other times they're full-on provocative lip-locks. (Such smooches have even been celebrated in songs like Katy Perry's 'I Kissed a Girl'!)

We were shocked by some of these stars going in for a little action (but not so surprised by some of them). From the iconic Britney Spears-Madonna-Christina Aguilera kisses to some famous movie hook-ups, we've got it all immortalized in the photos and videos of celebrity girls kissing girls below.

Britney Spears and Madonna

Frank Micelotta, Getty Images

Rihanna and Katy Perry

Jeff Kravitz, FilmMagic

Miley Cyrus and Cara DeLevingne

Twitter

Sandra Bullock and Scarlett Johansson

Jeff Kravitz, FilmMagic

Brittany Snow and Sophia Bush

YouTube

Miley Cyrus and Katy Perry

Madonna and Christina Aguilera

Scott Gries, Getty Image

Britney Spears and Rihanna

Ethan Miller, Getty Images

Natalie Portman and Mila Kunis

YouTube

Selma Blair and Sarah Michelle Gellar

SGranitz, WireImage

Heather Morris and Naya Rivera

YouTube

Mischa Barton and Olivia Wilde

YouTube

Meryl Streep and Sandra Bullock

Kevin Winter, Getty Images

Amanda Seyfried and Megan Fox

YouTube

Alanis Morissette and Sarah Jessica Parker

YouTube

Courteney Cox and Jennifer Aniston

Nikki Reed and Evan Rachel Wood

YouTube