London - Liverpool have completed the signing of Adam Lallana after the Southampton and England midfielder successfully underwent a club medical on Tuesday.
The transfer fee agreed by Southampton for the 26-year-old midfielder is believed to be around 25million (31million euros) and he will be on a five-year contract.
Lallana is Brendan Rodgers' third signing of the summer following to Anfield his Southampton team-mate Rickie Lambert and Bayer Leverkusen midfielder Emre Can, whose move from Germany will be ratified on Tuesday with the official opening of the transfer window for registrations.
"I'm so excited for the next chapter of my career, coming to a special club like Liverpool," Lallana told liverpoolfc.com.
"I hope I can add something to the team and hopefully we can win trophies while I'm here, because that's why I'm here -- for success."
Liverpool came up just short in their quest to win a first English title in 24 years last season, finishing runners-up in the Premier League to Manchester City.
But Lallana, a boyhood fan of Liverpool's city rivals Everton, said the way in which the Reds had played last term had left him wishing for a move to Anfield.
"Watching the run-in towards the end of last season it was unbelievable," he said. "It got the hairs on the back of my neck standing up just watching the style of football.
"Deep down I was thinking to myself 'One day hopefully I'll be able to play in that team'."- 'Special commodity' -
Liverpool manager Brendan Rodgers added: "What is apparent about Adam is that his character is on a par with his talent.
"He has leadership skills and personal qualities that make him a special commodity and I am delighted we have acted decisively to make sure he is wearing a Liverpool shirt next season."
With 18-year-old full-back Luke Shaw -- like Lallana a member of England's World Cup squad -- having also left Southampton, in his case for a teenage record 30m move to Manchester United, the Saints have seen three key players leave the south coast club following a season where they finished a promising eighth in the Premier League.
But with their coffers freshly swelled by the departure of former captain Lallana, Southampton promised new manager Ronald Koeman -- who took over after Mauricio Pochettino, now the manager of top-flight rivals Tottenham Hotspur, also left St Mary's after the end of last season -- would be allowed to use the income to bolster the squad.
"The fee received from Liverpool, although undisclosed, will allow the club to further develop the first-team squad for the 2014/2015 season," a Southampton statement said.
Lallana added the prospect of playing in the Champions League was too tempting to turn down.
"I am grateful Southampton accepted the offer in the end and granted my wish to play at such a fantastic football club with Champions League football and competing for Premier League titles.
"They are different targets to those of a club like Southampton.
"Five or six years ago I was playing League One but it is reality we've climbed up the leagues and done so well, and I'd like to think I'm here on merit."
Now both Lallana and Lambert are set to make their Liverpool debuts at home to Southampton, who visit Anfield on the opening day of the new league season.
"It would have been worse if it had been at St Mary's so I'm glad it is at Anfield," said Lallana.
"It is fate to be lining up against your former team-mates; Ricky said he would have bet his mortgage on it," he added.