Ever since we launched Gmail, we've tried to show relevant and unobtrusive ads. We're always trying to improve our algorithms to show better, more useful ads.

When you open a message in Gmail, you often see ads related to that email. Let's say you're looking at a confirmation email from a hotel in Chicago. Next to your email, you might see ads about flights to Chicago.

But sometimes, there aren't any good ads to match to a particular message. From now on, you'll sometimes see ads matched to another recent email instead. For example, let's say you're looking at a message from a friend wishing you a happy birthday. If there aren't any good ads for birthdays, you might see the Chicago flight ads related to your last email instead.

To show these ads, our systems don't need to store any extra information -- Gmail just picks a different recent email to match. The process is entirely automated: no humans are involved in selecting ads, and no email or personal information is shared with advertisers.

We've updated a help center article and a few faqs where we had specified that ads alongside an email were related only to the text of the current message. This doesn't change the Gmail privacy policy. We've also created this short video explaining the change:

We'll be rolling this out over the next few days. With this change, we hope you see better ads in Gmail -- more of what you're interested in and less of what you're not.