In snaps shared online, Taylor looks like she's having a blast and her companions are some of the most famous people in the music industry.
Can you spot them all?
In one, the 'I Knew You Were Trouble' singer is posing with music royalty Beyoncé, Jay-Z, Sam Smith and Justin Timberlake - that's some Very Important People in one room!
Wearing a cute tartan two-piece and a Santa hat, Taylor threw a huge party at her New York City apartment.
Nick Jonas and his girlfriend Olivia Culpo also joined in on the photo action, later sharing the snap with their Twitter fans alongside the message: "Happy Birthday @taylorswift that was so fun last night! @oliviaculpo."
Charli XCX and Kelly Osborne donned costume sunglasses, crowns and funny hats to pose with Taylor, too.
Singer Charli XCX wrote: "Owww my thighs ache so much from dancing last night! ps: @taylorswift13 happy birthday, ur a true sweetheart."
Actress and singer Selena Gomez, model Karlie Kloss, Emma Roberts and Jaime King were also present at the showbiz shindig.
Birthday girl Taylor told fans: "So this is being 25..... #WHAT #bestbirthdayEVER."
She also shared a cute photo of herself as a child reading The Tale Of Peter Rabbit book.
Alongside the throwback picture, Taylor joked: "Plotting, planning, HUSTLING since 1989."
Happy birthday Taylor!
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