Two of the biggest online real estate companies are joining forces.

Zillow announced today that it’s buying rival Trulia for $3.5 billion in stock. The two companies will maintain their separate brands, but Trulia CEO Pete Flint will report to Zillow CEO Spencer Rascoff. The deal is expected to close in 2015.

While it may seem a tad anticompetitive — Zillow currently has 83 million users and Trulia has 54 million — the two companies claim their customers don’t overlap much: Around half of Trulia’s users don’t visit Zillow, and around two-thirds of Zillow users don’t use Trulia’s products. That’s a sign that many consumers likely end up sticking with a single real estate solution.

So how will teaming up help? The companies say their total revenue accounts for less than 4 percent of the estimated $12 billion real estate ad industry, so there’s a big opportunity for growth there. Joining forces will also let the companies be more efficient — they expect to save $100 million in costs by 2016.

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During a conference call with media today, Rascoff noted that Zillow currently focuses on gathering information about all homes, making it ideal for both home seekers and current owners, while Trulia’s products are more focused on finding rentals and potential sales. Over time, he expects both brands to evolve further into those use cases.

“In a lot of places I think the Trulia experience is better than the Zillow experience, in other places I think Zillow’s experience is ahead,” Rascoff said, while praising Trulia’s mobile apps.

Bloomberg first reported last week that a potential acquisition between the two companies was in the works. Last year, Zillow bought the NYC real estate site StreetEasy for $50 million.

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