Others Online, a Seattle online advertising startup led by Jordan Mitchell, has been sold to the Rubicon Project in a deal of undisclosed size. As part of the deal, Mitchell is joining the Los Angeles company as vice president of data intelligence.

Others Online created a way for companies to better understand their audiences by tracking what users were reading or posting on the Web. It then offered targted advertisements to those users based on their personal interests.

The Rubicon Project is a heavily-funded startup that has developed a method for publishers to make money on unsold ad inventory, an arena that the recently-launched 5to1.com is also playing in.

[Post updated with a short Q&A with Others Online founder Jordan Mitchell]

The acquisition of Others Online will enhance The Rubicon Project's ad optimization system, the companies said.

In a press release, Mitchell added that the end goal is to help publishers make more advertising revenue.

"We were looking to partner with a company that was going to use our technology on a massive global scale, and we found that indeed with the Rubicon Project," he said. "Together we will create tremendous opportunity for premium publishers by making sure every impression generates them the most revenue possible.”

It is unclear whether Mitchell will be relocating to L.A., though he just arrived there this morning and promised to respond to some of our questions in the next hour or two.(We will update when we hear back).

The Rubicon Project -- founded in 2007 and led by online advertising guru Frank Addante -- has raised $33 million from investors such as Clearstone Venture Partners, Mayfield Fund, and IDG Ventures. The company's core business is profitable with more than $100 million in revenue managed so far in 2009.

UPDATE: Here's a short email Q&A I conducted with Mitchell today.

Just wanted to get some quick details on the acquisition -- why sell out now? "The market opportunity is now, and we needed global scale to realize it. Working with the Rubicon Project gives us that. The company serves more than 1500 premium publisher customers, optimizes more than 45 billion ads each month across hundreds of demand sources (ad networks, exchanges, audience sales reps) and reaches more than 500 million unique Internet users. They have amassed one of the largest sources of ad inventory and reach on the Internet and are the preferred source of targeted, audience-segmented inventory for ad networks and other resellers, many exclusive, around the world. It was an obvious fit. No other company in the space has their reach or their technology advantage, which will now be even stronger for their publishers with the acquisition of our technology. It’s truly a 1+1=3 situation.

Will you stay in Seattle or move to LA as part of the deal? We will be staying in Seattle, but commuting on a regular basis to LA.

How many employees did you have? And how much cash did you raise? Was this a good financial outcome for you? Although we’re not disclosing the terms of past fundraising efforts or the acquisition, we can say that our team and our investors couldn’t be more pleased.

Any other thoughts on this deal? This acquisition, which we consider to be an extremely positive outcome from a lot of hard work, couldn’t have been possible without the incredibly capable team that was Others Online. I’d like to especially recognize the hard work and dedication of Mike Dierken, Neal Richter and Sam Tingleff – these guys rock!