Liverpool have completed the £35m signing of England midfielder Alex Oxlade-Chamberlain from Arsenal.
The 24-year-old, who rejected a move to Chelsea on Tuesday after a fee had been agreed, joins on a five-year contract worth £120,000 a week.
Oxlade-Chamberlain, who was in the last year of his Arsenal contract, rejected a new deal worth up to £180,000 a week to stay at the Emirates.
He has started each of Arsenal's four games so far this season.
Oxlade-Chamberlain made 198 appearances for Arsenal since joining them from Southampton in August 2011, scoring 20 goals.
"I know my choice might come as a surprise to many, and the decision to leave was tough after being a part of the club for so many years, but I feel that this move is right for the next stage in my ongoing development, " he said in an Instagram post.
Liverpool boss Jurgen Klopp said he was "really happy" to have signed an "exciting" talent he "didn't need to think twice" about.
The German described Oxlade-Chamberlain as a "positive" player who is "willing to take risks" and "has the mentality and desire to get even better".
He added: "This is someone making a tough decision to leave one great club and come to another great club and I think he had many options, so to get him means I am delighted.
"He didn't make an easy decision but I think he made a great one to go on this journey with this squad of talented boys and our great supporters. I welcome him to the Liverpool family."
Meanwhile, Belgium striker Divock Origi has completed a season-long loan move to Bundesliga side Wolfsburg. The 22-year-old has scored 21 goals in 77 appearances for the Reds.
Liverpool's summer transfers
So far this summer, Liverpool have signed winger Mohamed Salah from Roma for £34m, full-back Andrew Robertson from Hull for £8m and striker Dominic Solanke after his contract at Chelsea expired.
Liverpool have also been pursuing Monaco's £75m-rated winger Thomas Lemar and Southampton centre-back Virgil van Dijk, while the Reds' Brazil forward Philippe Coutinho remains Barcelona's number one transfer target.
The 22-year-old is highly rated by Reds manager Jurgen Klopp but the arrival of Oxlade-Chamberlain means his chances in attack are likely to be restricted this season.
Origi wants regular football throughout Belgium's build-up to next summer's World Cup and Liverpool will also be eager to see the talented young forward continue his progress, so it is expected he will leave Anfield before the deadline.
Other former Saints at Anfield
Nathaniel Clyne (Southampton to Liverpool, July 2015m, £12.5m)
Dejan Lovren (Southampton to Liverpool, July 2014, £20m)
Sadio Mane (Southampton to Liverpool, July 2016, £34m)
Adam Lallana (Southampton to Liverpool, July 2014, £25m)