The 22-year-old has joined from Cardiff City in an £8m deal after agreeing terms on a four year deal and passing a medical at Loftus Road on Tuesday.
Caulker was a regular with Cardiff City last season
He will now link up with the rest of Harry Redknapp’s squad in Germany, where they are currently on tour ahead of the new campaign.
Working under Redknapp is nothing new to the former England U19 and Under-21 international, who began his career at Tottenham Hotspur under the former West Ham United and Portsmouth boss.
And it’s also a move back to familiar territory for the Feltham-born centre-half, who grew up in west London and joins former England and Manchester United defender Rio Ferdinand among the summer arrivals at Loftus Road.
"Steven is young, he's a good age and he's already a fine player - but he has so much more potential and it's a really excellent signing for the club," said Redknapp.
"He's got everything to be a top, top centre-half, so I couldn't be more pleased to have him.
"I want lads that want to have a go - you just have to hope you can get them.
"In the main I like players that have played in England and proved they can do it here rather than wait six months to see if they settle in - we haven't got six months.
"We need to stay in the league this year so we know what we are getting with the Caulkers and the Rios."
Caulker added: "Harry was very keen for me to join and that was a big plus, knowing the manager wants you.
"As for Rio, he has been a role model of mine for many years and to have the opportunity to play alongside him was something I felt I couldn't miss out on."
Caulker made his senior Three Lions debut in the game with Sweden in November 2012, a match which ended in a 4-2 defeat although Caulker did get his name on the scoresheet.
And Redknapp hopes that Caulker can start to challenge for a place in Roy Hodgson’s squad again, after spending last season battling against relegation with Cardiff.
"I think he [Caulker] feels if he was playing with Rio, it could help him get back into the England team," he added.
