Surrey wicketkeeper-batsman Steven Davies will join Somerset on an three-year deal from next season after he rejected a new contract at The Oval.
The England international, 30, joined Surrey from Worcestershire in 2009.
He has scored 10,878 runs in 182 first-class matches, including 21 centuries.
"He is a player of high class. Steven still harbours ambitions of playing for England and we will all work hard to support him," director of cricket Matt Maynard told the club website.
Davies has been second-choice keeper to Ben Foakes at Surrey this summer.
"I have made no secret of my desire to play for England again and I hope that a new challenge along with a return to wicket-keeping will help kick my career onto the next level," he said.
The left-hander will make his last appearance for Surrey in Saturday's One-Day Cup final against Warwickshire, having scored 373 runs to help the county reach Lord's.