The acquisition is part of an aggressive effort by the Rubicon Project to further build out its platform to deliver web publishers the most effective monetisation of their audiences and inventory.
Jordan Mitchell, CEO and founder of Others Online, will become the Rubicon Project's vice president of data intelligence.
Mitchell said: "Currently the marketplace is fraught with inefficiency, lack of standardisation, varying data quality and overlap issues.
"We built Others Online to specifically help publishers leverage data to make more money.
"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.
"Together we will create tremendous opportunity for premium publishers by making sure every impression generates them the most revenue possible."
The Rubicon Project launched in early 2007 to automate and optimise the buying and selling of online advertising.
"The company developed an ad network optimisation service, which has enabled web publishers to make more money from unsold ad inventory.
Frank Addante, CEO and founder of the Rubicon Project, said: "There are two new challenges facing the online ad industry -- audience and data fragmentation.
"Advertisers need to connect directly with their audiences. Fragmentation has made it difficult for them to efficiently reach their audiences.
"Further, the recent growth in the number of data companies in the market has created fragmentation at the data level.
"Given our massive scale, we have taken a giant step toward solving the audience fragmentation problem.
"As a result, we have become a central place for ad networks, exchanges, publishers and audience rep firms to transact.
"Our platform has become a prime channel for many data companies to reach their customers and audiences.
"The acquisition of Others Online will help us solve the data fragmentation challenge to the benefit of everyone connected to the Rubicon Project platform."