Facebook’s new Timeline profile began rolling out to users in several countries on Wednesday night. It appears that typing “Timeline” in the Facebook search bar returns a result for “Introducing Timeline,” which leads to a page explaining the new format and providing an option to upgrade.

Facebook launched Timeline in New Zealand last week, but did not provide a worldwide release date. We are awaiting details from Facebook about the scope of today’s launch, but according to a message displayed when users request to preview the new layout, Timeline will go live on Dec. 21. This gives users a week to preview their Timelines before making them visible to friends and others. [Update 12/15/2011 10:20am PST: Facebook clarified that the opt-in period for Timeline will last for a few weeks. However, from the time users activate the new profile, they will have seven days to review their content before anyone else will see it. If users want to publish their timelines right away, they can.]

[Update 12/15/2011 8:15am PST: Facebook has confirmed the global launch of Timeline. Starting today the new profile will also be available on Android and m.facebook.com. For more information about the changes, see Inside Facebook's complete walk-through of Timeline.]

After debuting the product at F8 in September, Facebook gave developers access to a beta version. Early adopters found a way to sign up as a developer and test Timeline for themselves, and according to a post on TechCrunch, more than a million users took advantage of this option.