James Foley (director of At Close Range): "Sean is one of the greats. And it's a shame he's become a director, because there are already too many directors out there, but not enough actors of his caliber".

Gary Oldman: "We were shooting in Times Square and all these newspaper photographers showed up, and they wouldn't stop. They took flash photographs while we were doing takes. I said, 'I don't mind you taking photographs, but don't do it while I'm working! 'Cause it ruins the film'. and they just wouldn't stop. There was this one particular guy, and I said to Sean, 'I'm gonna go whack this guy out!' And Sean was just...he waved it all aside. What a life!".

Rick Rosenthal (director of Bad Boys): "The only reason that people compare Sean to Robert De Niro is that Sean is the only actor of his generation who can really become a different person for each acting job".

John Schlesinger (director of The Falcon And The Snowman): "I find Penn quite difficult, but he really gets into the skin of the character he's playing. And as Daulton Lee resists all authority, so Sean naturally hated me. I must say that the feeling was reciprocated, although I thought he was marvelous in the film".

Robin Wright:" When I read the screenplay  of The Crossing Guard for the first time, I started crying. That's what I want in a movie. Emotions. Emotions and a message. As a director, Sean is great, since he's a great actor. He knows what an actor needs. Working with him is wonderful, he makes you feel comfortable".

Timothy Hutton: " I've spent time with Sean and his family. They're a very solid family, and they also know how to get under each other's skin. They're very real with each other. Nobody gets away with anything when they're around each other. It's great. Sean is very honest and very loyal. You get the sense with Sean that friendship is a lifetime thing".

Tim Robbins: "I didn't find him far removed from us at all. From the first day he laughed, he joked. In between takes, he'd break character. I'd heard stories about him, but they were totally unfounded - that bullshit about having to refer to him as his character's name. That stuff usually comes from a source that has a personal vengeance involved. I asked him about it, and it came from a particular director or producer who he'd gotton into a difficult situation with. Total bullshit. One word that I would say is real key to understanding Sean is honesty".

David Morse: "Sean has a great loyalty that really knows no bounds".

Oliver Stone: "Not everyone hates Mr. Cool (Sean). Not across the board. People respect him. Sean is excellent on performance."