After a leak by Siri earlier this morning, Apple have now confirmed that this year's World Wide Developers Conference will kick off from June 13:

"The Apple Worldwide Developers Conference kicks off June 13 in San Francisco. WWDC features more than 100 technical sessions, over 1,000 Apple engineers, hands-on labs, and the Apple Design Awards."

Apple are expected to announce new versions of it mobile and desktop operating systems at the Keynote to kick-start the conference.