Facebook, the biggest social network in the world, now has over 1.5 billion monthly active users. According to David Kirkpatrick’s book The Facebook Effect, the company was a very popular M&A target in its startup years.

As early as 4 months after Facebook’s inception, people with money and people representing companies with money began lining up to beg Facebook co-founder and CEO Mark Zuckerberg to take their cash and sell the company. Obviously, Zuckerberg turned all their offers down. But some offers were much more tempting than you probably realize.

Meet the 10 companies that tried to buy Facebook back when it was a startup…

Facebook, then called TheFacebook.com, went live in February 2004. Just four months later and prior to any outside investment, a 20-year-old Mark Zuckerberg fielded a $10 million offer from an unnamed New York financier.

“He didn’t for a minute think seriously about accepting,” writes David Kirkpatrick in The Facebook Effect.

According to some documents Business Insider has seen, one early bidder for Facebook was Friendster. But the deal was dependent on Friendster raising another round before Facebook got big on its own. Never happened.

Mark and his Harvard dorm-mates rented a house in leafy Palo Alto during the summer of 2004. It wasn’t long before “a couple of Google executives came over to see if there might be a way to work with or even buy TheFacebook,” Kirkpatrick reports in The Facebook Effect.

During Spring 2005, Facebook (still TheFacebook) was talking to The Washington Post Company about an investment. Out of nowhere, Viacom offered $75 million to buy the company. Mark would have earned $35 million on the spot, reports Kirkpatrick.

Instead, then Facebook president Sean Parker used the offer to haggle better terms out of the Post (which eventually got scooped on the deal by Accel Partners anyway).

In the spring of 2005, MySpace CEO Chris DeWolfe visited Mark and his team to “put out feelers about possibly buying TheFacebook,” Kirkpatrick reports. Zuckerberg, his president Sean Parker, and adviser Matt Cohler met with Chris, “but only because they thought he was an interesting guy and they were curious about MySpace.”

In January 2006, then News Corp digital boss Ross Levinsohn flew Mark Zuckerberg and one of his top advisors, Matt Cohler, to Los Angeles. Levinsohn wanted to buy TheFacebook, but he worried it might not keep up its growth.

“That’s the difference between a Los Angeles company and a Silicon Valley company,” Mark Zuckerberg says in The Facebook Effect, “We built this to last, and these guys (at MySpace) don’t have a clue.”

Viacom hadn’t given up on Facebook yet in late 2005. Focus groups told them that MTV viewers were spending more and more time on the site. So that fall, Mark flew to New York to meet with CEO Tom Freston. Tom pitched all kinds of synergies between MTV and Facebook. Mark wasn’t interested.

“It was a no-thank-you meeting,” a source tells Kirkpatrick.

Kirkpatrick doesn’t offer many details, but apparently NBC executives stopped by for a peek in 2005.

In early 2006, MTV boss Michael Wolf stopped by Facebook one last time. Zuckerberg told him he thought the company was worth $2 billion. A couple weeks later, Viacom sent Facebook a $1.5 billion offer – $800 million in cash up front, the rest a payout later.

Facebook almost sold, according to The Facebook Effect, but it wanted a bigger upfront payment. Viacom’s CFO was nervous about paying so much for a company with such small revenues. The deal fell apart. Viacom never came back.

In the summer of 2006, Yahoo decided to offer Facebook $1 billion. Facebook’s investors and many of its executives wanted to sell. But Facebook was about to launch the News Feed, and if it went well, Mark Zuckerberg figured the company would be worth way more than a $1 billion.

In any event, Yahoo lowered its offer to $850 million after announcing horrible Q2 earnings. Facebook’s board took 10 minutes to reject the lowered offer, according to The Facebook Effect.

AOL CEO Jonathan Miller decided he wanted to buy Facebook in the middle of 2006. He even convinced Time Inc CEO Anne Moore to come in on the deal before he took it to AOL’s parent company, Time Warner. His plan: AOL would sell MapQuest and Tegic. Time Inc would sell IPC. Together they’d offer $1 billion-plus. Time Warner CEO Jeff Bewkes nixed the idea.

Kirkpatrick writes, “He said if they could live without those properties they should go ahead and sell them, then turn the cash over to the parent company.”

In the fall of 2006, Yahoo came back to Facebook and suggested it would pay $1 billion or more. But by then, Facebook had opened the site to people beyond college and high school students. Registrations were up from 20,000 a day to 50,000 a day, Kirkpatrick reports. Even eager-for-an-exit VC and Facebook investor Jim Breyer was OK with passing on the deal.

One guy who wasn’t, Facebook COO Owen Van Natta, was also not long for the company.

In fall 2007, Google’s top ad salesman Tim Armstrong convinced the company’s board to let him pursue a deal in which Google would serve Facebook’s international ads. “The board even approved talks about buying (Facebook), if it made sense,” writes Kirkpatrick.

Google never got the deal, but its offer to invest in Facebook at a $15 billion valuation would re-shape Mark Zuckerberg’s company forever.

Determined to keep Facebook away from Google, Microsoft CEO Steve Ballmer offered to buy the company in 2007. Steve knew Mark would never relinquish control over Facebook, so he came up with a deal based on Hoffman-LaRoche’s acquisition of Genentech.

Kirkpatrick explains, “Microsoft (would) acquire a small stake in Facebook at a $15 billion valuation. Then, Microsoft would have the option, every six months, to buy another 5% of Facebook. A complete takeover of the company would take 5 to 7 years.”

The acquisition never happened, but Microsoft did buy 1.6% of Facebook for about $250 million. That deal, which set Facebook’s value at $15 billion, stipulated that Facebook would have to give Microsoft notice if it ever began to take a buyout offer from Google seriously.

One reason: Microsoft’s $247 million investment, which set Facebook’s value at astronomical $15 billion, stipulated that Facebook would have to give Microsoft notice before it ever considered a buyout offer from Google – just about the only other company in the world that could pay so much for a tech startup with no revenues.