Ernest Joseph "Trey" Anastasio III (born September 30, 1964) is an American guitarist, composer, and singer-songwriter best known as the lead guitarist of the rock band Phish, which he co-founded in 1983. He is credited by name as composer of 152 Phish original songs, 141 of them as a solo credit, in addition to 41 credits attributed to the band as a whole.

In addition to his work with Phish, Anastasio has released 11 solo albums, and been part of several side projects including the Trey Anastasio Band, Oysterhead, Ghosts of the Forest, Phil Lesh and Friends, and Surrender to the Air.

He has performed his own compositions with the New York Philharmonic, the Los Angeles Philharmonic, the Baltimore Symphony Orchestra, the Atlanta Symphony Orchestra, the National Symphony Orchestra, and many others. With Amanda Green, he wrote the score for the Broadway musical Hands on a Hardbody. In 2013, they were nominated for a Tony Award for Best Original Score at the 67th Tony Awards, and were awarded the 2013 Dramatists Guild Frederick Loewe Award for best theatrical score composition.

In 2023, Rolling Stone ranked Anastasio at number 53 on their list of the 250 greatest guitarists of all time.