The Calendar team was the first to launch its Google Data API back in 2006, and in that proud tradition, we're excited to offer an additional way for developers to read from, and write to Google Calendar: the CalDAV protocol. (CalDAV — an extension of WebDAV — is an evolving, open standard for calendar synchronization.)

So far we've focused on Apple's iCal 3.0 as a first working example of 2-way Google Calendar sync over CalDAV.* But we're calling all current and prospective CalDAV developers to help us firm up the implementation, and make it play nice with other popular CalDAV-friendly clients.

For information on how Google Calendar data maps to the CalDAV protocol, please check out our CalDAV developer's guide. And of course, don't hesitate to hurl feedback in the general direction of our Google Group.

* Disclaimer: during this developer-focused release, and in light of known issues, we strongly suggest that you restrict Google Calendar <> iCal 3.0 synchronization to test accounts only.