Brazil right back Daniel Alves completed his move from Sevilla to Barcelona on a four-year contract on Wednesday.
The club said they had paid 29 million euros with a further six million dependent on appearances and results, for the 25-year-old international.
"We have signed the best player in his position in the world. He is a full back who likes to attack and offers a great all-round contribution," Barca sports director Txiki Begiristain told a news conference.
Alves was an outstanding figure at Sevilla in his five and a half seasons there helping them to win two UEFA Cups, a King's Cup, a European Super Cup and a Spanish Super Cup, making him a target for a number of Europe's top clubs.
Alves said: "Barcelona want to return to be the side they were two years ago (when they won a second consecutive Primera Liga title and the European Cup) and I am honoured they have come for me to form a part of this project."
The Brazilian is the club's fourth signing since they finished third in the league in May, to end their second consecutive season without silverware.
Barca sacked coach Frank Rijkaard in favour of former player Pep Guardiola, and have moved swiftly to reinforce their defence primarily, landing centre-backs Martin Caceres and Gerard Pique and defensive midfielder Seydou Keita, also from Sevilla.
Spanish media have reported Barca are also interested in signing Arsenal midfielder Aleksandr Hleb and striker Emmanuel Adebayor, and Zenith St Petersburg's Russian attacker Andrei Arshavin.Reuse content