Arsenal have signed Thomas Partey from Atletico Madrid on Deadline Day after meeting his £45m release clause.
Partey signed a long-term deal at the Emirates after he completed his medical and paperwork just before Monday's 11pm deadline.
He will wear the No 18 shirt and will join up with his new team-mates next week after he returns from international duty with Ghana.
Partey has been a key player in Diego Simeone's midfield since breaking into the first team from Atletico's academy in 2015.
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."
Partey becomes Arsenal's seventh signing of the summer, with the club having already signed Willian on a free transfer from Chelsea and defender Gabriel from Lille for £27m.
The Gunners also agreed permanent deals for defenders Cedric Soares and Pablo Mari, who had been on loan at the club, and extended the loan deal for Dani Ceballos from Real Madrid for a second year.
Goalkeeper Alex Runarsson was the club's sixth signing, joining from Ligue 1 club Dijon on a four-year deal.
In recent weeks, Arsenal also moved for Lyon midfielder Houssem Aouar but after their offer was rejected they turned their attention back to the Atletico midfielder.
Lucas Torreira has moved in the opposite direction to Atletico Madrid in a loan deal until the end of the season and Matteo Guendouzi has signed for a German club Hertha Berlin on a season-long loan.
Partey signed a long-term deal at the Emirates after he completed his medical and paperwork just before Monday's 11pm deadline.
He will wear the No 18 shirt and will join up with his new team-mates next week after he returns from international duty with Ghana.
Partey has been a key player in Diego Simeone's midfield since breaking into the first team from Atletico's academy in 2015.
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."
Partey becomes Arsenal's seventh signing of the summer, with the club having already signed Willian on a free transfer from Chelsea and defender Gabriel from Lille for £27m.
The Gunners also agreed permanent deals for defenders Cedric Soares and Pablo Mari, who had been on loan at the club, and extended the loan deal for Dani Ceballos from Real Madrid for a second year.
Goalkeeper Alex Runarsson was the club's sixth signing, joining from Ligue 1 club Dijon on a four-year deal.
In recent weeks, Arsenal also moved for Lyon midfielder Houssem Aouar but after their offer was rejected they turned their attention back to the Atletico midfielder.
Lucas Torreira has moved in the opposite direction to Atletico Madrid in a loan deal until the end of the season and Matteo Guendouzi has signed for a German club Hertha Berlin on a season-long loan.