ABC News President David Westin broke the news in an e-mail to staffers this morning:

"After 42 years with ABC News and 25 years as anchor and managing editor of Nightline, Ted Koppel has advised me that he intends to leave the network at the end of his current contract, which expires on December 4th of this year. His long-time executive producer, Tom Bettag, will also be leaving.

"Ted, Tom, and I have had ongoing conversations for almost five years seeking to ensure Nightline's continuity and to create an orderly transition. All of us are optimistic that both goals can and will be achieved. Ted and I have discussed a number of options under which he might have remained at Nightline or in some other capacity at ABC News, but Ted believes this is the right time for him to leave. As much as I will regret his leaving, he is firm in his conviction, and I respect his decision.

There will be ample opportunity, closer to the time of their departure, for me to express fully what Ted and Tom have meant to ABC News and to network news overall. For 25 years, Ted Koppel and Nightline have represented the best of what we can achieve in reporting on the important and difficult issues of our day - all done with the utmost intelligence and integrity. By making this announcement well in advance, Ted and Tom have provided us with the time we need to segue to the next chapter in the illustrious history of Nightline."