Paulinho, the Brazilian midfielder, passed a medical last night and completed his £17m move from Corinthians to Tottenham.
The 24-year-old, who scored 34 goals in 167 games for the São Paulo-based club, was one of the outstanding Brazil players in their Confederations Cup victory on home soil last month.
"I want to thank Tottenham for believing in me," he said. "It's a huge pleasure for my career to be at a club as big as Tottenham and I know it will be a huge challenge.
"I used to watch Premier League matches in Brazil – including Tottenham games – and this club has big players. I just want to help them to succeed here."
Paulinho has been capped by Brazil 17 times and was part of the Corinthians side that beat Chelsea in the Club World Cup final last December. He is Andre Villas-Boas' first signing of the summer and joins fellow Brazilian midfielder Sandro at White Hart Lane.
Aston Villa's goalkeeper, Brad Guzan, has signed a new four-year contract which ties him to the club until 2017. The 28-year-old American international, who replaced Shay Given as the club's first choice last season, said: "This is just the start now, the start of hard work. We have to build on last year and go forward. For me, it's an honour and a privilege to play for Aston Villa and commit my future long term."
Guzan joined Villa in July 2008 from the American side Chivas and had to bide his time as reserve goalkeeper behind both Brad Friedel and then Given before being handed his opportunity. "Brad has been exceptional for the club, really fantastic on and off the pitch," Paul Lambert, the Villa manager, said.
Guzan's United States team-mate, Jozy Altidore, is set to join Sunderland from AZ Alkmaar after the two clubs reached agreement over a transfer for an undisclosed fee.
The 23-year-old, who scored 38 goals in two seasons for AZ, must still agree personal terms and pass a medical. The move marks a return to the Premier League for the striker, who managed just a single goal in a season-long loan spell at Hull City in 2009-10. Altidore moved from New York Red Bulls to Villarreal in 2008 before joining AZ in 2011.