Haitink was already scheduled to lead the CSO for a week in October; he has now added an additional program in May 2007, replacing Manfred Honeck. Starting in 2007-08, he will lead four to six weeks of performances each season, including concerts at Carnegie Hall, the BBC Proms, and the Lucerne Festival.

Boulez will lead three to four weeks of programs per season in his new position.

"The Chicago Symphony Orchestra family is very excited to celebrate both its newly formed relationship with Bernard Haitink and the continuation of its long standing relationship with Pierre Boulez," said CSO president Deborah R. Card. "Our strong commitment to maintaining the high quality of music making for which the CSO is known is further strengthened by the appointment of these two distinguished masters. We are thrilled that these gentlemen have agreed to collaborate with us as key members of the CSO's artistic team."

In a press release, the orchestra said that in the absence of a music director, Haitink will "lend his expertise and ideas on artistic matters." Boulez will "assume additional behind-the-scenes responsibilities, working with the musicians of the orchestra and management team, participating in auditions for open positions, and assisting with personnel issues as they arise."

Haitink is 77; his storied career includes a long stint as music director of Amsterdam's Royal Concertgebouw Orchestra and posts at the Dresden Staatskapelle, the Royal Opera, Glyndebourne, and the London Philharmonic. He also served as principal guest conductor of the Boston Symphony, where, in an arrangement similar to his new post in Chicago, he bridged the gap between the Seiji Ozawa and James Levine eras.

Boulez, 81, founded the Paris new-music institution IRCAM and has been principal guest conductor of the Cleveland Orchestra, chief conductor of the BBC Symphony, and music director of the New York Philharmonic.