As reported earlier, Google is merging YouTube friends with Address Book contacts. Now, the company has put out an announcement that it is integrating Contacts and Gmail with Google+.

Not only does this represent the continued merger among Google user-identifying products, it represents increased integration of Google+ into Gmail, which has been expected since Google+ first launched. It may not be the last integration we see between Google+ and Gmail, but it certainly illustrates the first major integration between the two, beyond the link in the navigation bar at the top of the screen.

Google+ users can grow their circles, filter emails and contacts by circles, keep contact info up to date automatically, and share photos to Google+ from Gmail and Contacts, Google says.

“Now when you open an email from someone on Google+, you can see the most recent post they’ve shared with you on the right-hand side of the conversation,” explains engineering director Mark Striebeck. “If they’re not in your circles yet, it’s easy to add them straight from Gmail.”

“Looking for the info on an upcoming family holiday gathering but can’t remember who sent it?” he continues. “If you’ve spent time building your Google+ circles, you can now quickly use them to filter your mail, saving yourself from having to sift through that pile of daily deal emails and newsletters. You can see messages from all of your circles at once or from each individual circle. And if you want, you can show circle names on emails in your inbox. Contacts can also be filtered by circles, making it easier to view your social connections.”

As you can see from the image above, Circles is in the left-hand menu now.

When users’ contacts have Google profiles, their contact entry in Gmail will be updated with the profile info they share. This includes phone numbers, email addresses, etc. If that contact info is changed on the profile at a later date, it will continue to automatically update in your contacts.

I’d be surprised if some people don’t freak out about this from the privacy perspective, but if the info is available on the profile, it’s out there anyway.

Gmail users can also share image attachments to Google+ from a simple share button that appears next to the usual “view” and “download” options.

The changes will be rolling out over the next few days. Google Apps users will have to wait a bit.

Related: Gmail’s new design is now out there for all.