Stars have taken to Twitter to remember the actor, who had starred in many acclaimed movies, including Magnolia, Mission:Impossible III, Boogie Nights, The Boat that Rocked, The Master and Moneyball.
He won a Best Actor Oscar for his role in 2005's Capote.
Hoffman leaves behind his partner of 15 years, Mimi O'Donnell, and their three children.
In a statement, his family said the "outpouring of love and support" was appreciated. They asked people to respect their privacy.
"We are devastated by the loss of our beloved Phil and appreciate the outpouring of love and support we have received from everyone," they said in a statement.