Neil Best has started seven games in the Premiership for Saints this season
Worcester Warriors have signed Ireland international flanker Neil Best from Northampton for the 2010/11 season.
The Premiership club have confirmed that Best has agreed a two-year deal.
The 30-year-old, who joined Saints in 2008, has played 18 times for Ireland, but has not been in his country's team since the 2007 World Cup.
Worcester have also confirmed that home-grown flanker Tom Wood is set to leave Sixways at the end of the season - and is expected to move to Leicester.
His destination has not been confirmed, but he has been linked with the Guinness Premiership champions.
Wood, who is a product of the academy at Sixways, was called into the England Saxons squad on Monday, along with Warriors wing Miles Benjamin.
Director of rugby Mike Ruddock told the club's website: "We are disappointed that Tom Wood will leave the club at the end of the season.
"But Neil Best is a highly respected figure in British and Irish rugby and brings with him a wealth of experience at international level and no-nonsense approach combined with intelligence and skill.
"Neil is just the sort of player we need in our squad and I know he will add leadership to our team and will always lead from the front."
Best joins Worcester on a two-year contract with an exclusive option on a third year.
The Belfast-born back row said: "Worcester has a real rugby feel to it, very much like Northampton, and the club is held in high esteem by the people who really want it to do well.
"Everyone is singing from the same hymn sheet and keen for success. That makes you want to play for the club.
"I will leave Northampton at the end of this season with very fond memories. I have lots of friends at the club and got on very well with the coaching staff.
"I'm a professional. I will do absolutely everything I can to make sure the club is now as successful as we can be this season."
Meanwhile, Warriors prop Matt Mullan has flown to Portugal after being called up by Martin Johnson to join the full England 2010 Six Nations squad.
England Saxons prop Mullan is in as cover for Andrew Sheridan, who is struggling with a shoulder injury.