Apple says its CEO, Steve Jobs, is resigning, effective immediately.
Jobs has now been elected as the company's Chairman.
Tim Cook will take on the role of CEO.
Cook had previously served as the company's Chief Operating Officer.
Jobs wrote a letter to the company's Board of Directors.
In it, he says, "I believe Apple's brightest and most innovative days are ahead of it."
"And I look forward to watching and contributing to its success in a new role."
Jobs has battled with health problems in the past.
In 2004, he revealed he had been diagnosed with and cured of a rare form of pancreatic cancer.
In the following years, Jobs took additional leaves for health reasons.
And each time, he emerged looking more and more frail.
Nicole Grether, The Associated Press.