Arsenal have signed Thomas Partey from Atletico Madrid on a long-term deal after paying his 50m euros (£45.3m) release clause.
The 27-year-old Ghana midfielder made 35 league appearances and scored three goals for Diego Simeone’s side as they finished third in La Liga last season.
He played 188 times for Atletico after joining the club in 2011.
Uruguay midfielder Lucas Torreira, 24, has moved in the opposite direction and joined the La Liga side on loan.
Arsenal have been linked with Partey, who has 29 international caps, throughout the summer transfer window.
Partey won the 2017-18 Europa League and 2018 Super Cup with Atletico and signed a new deal at the Wanda Metropolitano in 2018, until the end of June 2023.
Arsenal manager Mikel Arteta said: “We have been watching Thomas for a while, so we’re now delighted to add such a high-quality player to our squad.
“He is a dynamic midfielder with great energy. He brings a lot of experience from a top club that has competed at the highest level in La Liga and the Champions League for several years.
“We’re very impressed with his attitude and his approach to the game. He’s an intelligent footballer and we’re looking forward to him integrating into our system and contributing to the progress we’re building at the moment at the club.”