"Your mother and I don't yet have the words to describe the hope you give us for the future," the post, structured as a letter from the couple, begins. "Your new life is full of promise, and we hope you will be happy and healthy so you can explore it fully. You've already given us a reason to reflect on the world we hope you live in."
As part of the announcement, Zuckerberg and Chan also pledged to give 99 percent of their Facebook shares to charity during their lives, through a new organization called the Chan Zuckerberg Initiative. At about $45 billion today, it's likely to be one of the biggest charitable pledges in history.
"It's been 37 weeks so I think it's time for her to come out," Zuckerberg joked in a video announcing the initiative, recorded before the birth and posted today.
Zuckerberg, last month, announced that he would be taking two months off for paternity leave.