Chelsea loan Ghana winger Atsu to Everton
Ghana midfielder Christian Atsu Twasam (L) vies for the ball with Germany forward Thomas Mueller at Brazil's Castelao Stadium during the World Cup on June 21, 2014 - by Carl de Souza
The two clubs confirmed the deal on Wednesday night after Atsu passed a medical. He could make his Everton debut in their Premier League opener at Leicester City on Saturday.
"I'm very happy to be joining Everton because it's a great club, which likes to play football, and it's a great pleasure to be here," Atsu told evertontv.
"Playing in the Premier League has always been a dream for me and I have achieved that dream.
"This is the biggest level for me to play at. I know that it's a very competitive league and I believe with hard work we're going to be successful this season."
Atsu joined Chelsea from Porto last year and spent the 2013-14 campaign on loan at Dutch side Vitesse Arnhem, with whom the London club have a strategic partnership.
He started all three of Ghana's matches at the World Cup in Brazil.
"He's a player who fits in with the culture and the way we want to play," said Everton manager Roberto Martinez.
"He's a left-footed player who loves taking people on and he's got a really good understanding of the game for such a young man."
Atsu is Everton's fourth close-season signing, following Gareth Barry, Muhamed Besic and record signing Romelu Lukaku -- who also arrived from Chelsea.