The surprise came Wednesday afternoon.
"If there ever came a day when I could no longer meet my duties and expectations as Apple's CEO, I would be the first to let you know," Jobs said in a statement. "Unfortunately, that day has come."
Jobs has battled serious health issues for several years now and stepped away from day-to-day duties months ago.
Here is the text of the letter he released:
To the Apple Board of Directors and the Apple Community: