Idina Menzel
The singer sang "Let It Go" with the Frozen star at her concert in Tampa, Fla. on Halloween...in costume!
Tove Lo
Taylor Swift surprised her sold-out Atlanta crowd with the "Talking Body" crooner.
Miranda Lambert
Blake Shelton's ex-wife joined Swift onstage to perform "Little Red Wagon."
Ellie Goulding
With just a few U.S. dates to go, Swift continued to surprise fans with an impromptu performance of "Love Me Like You Do" in Texas.
Charli XCX
The "Boom Clap" crooner joined her friend on stage for another electrifying performance in front of 50,000 fans.
Keith Urban
Goin' country in Toronto! Swift brought out the American Idol judge.
Nelly
During the St. Louis show, T.Swift and the hometown rapper had a blast singing his greatest hits.
Mick Jagger
Swift proved she had moves like Jagger when she brought the Rolling Stones frontman on stage in Nashville to sing "Satisfaction."
Steven Tyler
Swift and the Aerosmith frontman sang his band's 1998 hit "I Don't Want to Miss a Thing."
Alison Krauss
At a concert in Nashville, Swift sang "When You Say Nothing At All" with the country star, who released a cover of the ballad in 1995.
Kelsea Ballerini
Swift and the country singer performed Ballerini's 2014 hit "Love Me Like You Mean It" in Nashville.
The Band Perry
The group performed "If I Die Young" at Bankers Life Fieldhouse in Indianapolis.
Wiz Khalifa
The two performed at the Minute Maid Park in Houston.
Avril Lavigne
The singer performed "Complicated" with the Canadian pop star at her concert in San Diego.
Selena Gomez
The singer brought her "Bad Blood" co-star and bestie on stage for her final Los Angeles show.
Justin Timberlake
At her final L.A. show, Swift asked the new dad to perform for the first time since baby Silas' birth.
Alanis Morissette
We're so jealous! Swift got to sing one of the most iconic breakup songs of all time ("You Oughta Know") with the person who wrote it.
Beck and St. Vincent
For one of her five sold-out Los Angeles shows, Taylor got some indie cred by having Beck and St. Vincent perform "Dreams" with her.
Ellen DeGeneres
The Emmy-winning talk-show host showed up in a sparkly tutu ensemble that rivaled Swift's.
Lorde
The besties performed a duet to "Royals" in Washington D.C.
Hailee Steinfeld, Gigi Hadid, Lily Alridge and Lena Dunham
Swift proved she rolled deep by having her squad join her during her New Jersey show.
Fetty Wap
At her Seattle show, Swift invited the rapper to sing his hit "Trap Queen" with her. She later shared an Instagram pic of the moment and claimed she was "unable to find my chill."
Martha Hunt, Kendall Jenner, Serena Williams, Karlie Kloss, Gigi Hadid, Cara Delevingne
Taylor's cameos for her London leg were a real model squad.
U.S. Women's Soccer Team
The World Cup-winning soccer team waved American flags while walking the catwalk during one of Swift's New Jersey stops.