Speaking about the move, Crouch said: "I am thrilled to be joining a club as prestigious and successful as Liverpool. Once I heard of their interest in me it was hard not to think about what it would be like to pull on the famous red shirt and play in front of the Kop, but I was also very aware of my responsibilities towards Southampton.
"After a lot of thought I requested the permission of the Chairman and Board of Directors of the club to talk to Liverpool. Southampton bought me from Aston Villa and allowed me to play regularly in the Premiership, resulting in an appearance for England in the summer. This helped my career tremendously and has now given me the opportunity to move to Liverpool and play on an even bigger stage, something that no-one could realistically expect me to turn down.
"Under almost any other circumstances I would have committed myself to helping Southampton regain their Premiership status. There is a great group of players at the club and I am sure they will be successful in the coming seasons.
"I am also very grateful to Harry Redknapp for everything he has done in my career to date, he made it clear he would not stand in my way over this transfer move. The Chairman hasalso handled the negotiations with both me and the other clubs professionally and fairly and I would like to thank both of them for the way they have conducted themselves during these discussions.
"I would also like to thank all the Southampton fans for their support and wish everyone at the club a successful season."
Crouch will wear the number 15 shirt for Liverpool.