Llewellyn has been music director of the society for five years.

Norrington, who is also chief conductor of the Radio Symphony Orchestra of Stuttgart and the Camerata Salzburg and was closely involved with the early seasons of the Boston Early Music Festival, will work with the society through the 2007-08 season, while the search for a new music director takes place.

"With his seniority and global view of the profession," Llewellyn said, "Roger will certainly bring something special here, and he is still a force in the land. He is the most outspoken member of that generation of early-music pioneers, so he will stir things up in a very positive way."