Jobs announced the move in an email to employees:
At my request, the board of directors has granted me a medical leave of absence so I can focus on my health. I will continue as CEO and be involved in major strategic decisions for the company.
I have asked Tim Cook to be responsible for all of Apple’s day to day operations. I have great confidence that Tim and the rest of the executive management team will do a terrific job executing the exciting plans we have in place for 2011.
I love Apple so much and hope to be back as soon as I can. In the meantime, my family and I would deeply appreciate respect for our privacy.
Jobs was diagnosed with pancreatic cancer and had reportedly been cured of the disease back in 2004. It's unknown whether Jobs' current medical condition is related to a similar leave of absence he took in January 2009 or his liver transplant in May 2009.
Jobs' health has been closely scrutinized by Wall Street and Apple hasn't announced when he'll return.