West Ham have signed Manchester United defender Jonathan Spector for an initial fee of £500,000.
Spector spent last season on loan at The Valley with Charlton
The 20-year-old American made just eight appearances after moving to Old Trafford in 2003 and spent all of last season at loan at Charlton.
He would have been part of the USA's World Cup squad but dislocated his shoulder playing for the Addicks.
"He has huge potential and we hope that bears fruition at West Ham," manager Alan Pardew told the club's website.
"He is a player we have been tracking for the past 18 months or so. He is definitely one for the future and, with the Uefa Cup campaign to look forward to, he will add to our defensive capacity.
"Having developed as a young player at Manchester United, he arrives with a fantastic pedigree.
"I was also very impressed by his character, which was a big factor in bringing him to the club."