Yammer is a freemium enterprise social networking service used for private communication within organizations. Access to a Yammer network is determined by a user's Internet domain so that only individuals with approved email addresses might join their respective networks.

The service began as an internal communication system for the genealogy website Geni.com, and was launched as an independent product in 2008. Microsoft later acquired Yammer in 2012 for US$1.2 billion.


Adam Pisoni, one of the co-founders of Yammer, in 2013.

On September 8, 2008, Yammer was launched at the TechCrunch50 conference after co-founder David Sacks, a former PayPal executive, developed the basic concept of Yammer while working on a startup project after he left PayPal in 2002. In addition to its communication function, Yammer additionally gives third-party developers the opportunity to create and sell their collaborative applications directly to users of the platform.

By April 2010, Yammer CEO Sacks claimed that Yammer revenue was doubling every quarter, but wouldn't disclose revenue figures for 2009 beyond describing it as "seven figures." Sacks additionally stated that 70 percent of Fortune 500 companies were using Yammer at that time.

In September 2010, the service was being used by more than three million users and 80,000 companies worldwide, including 80 percent of the Fortune 500. During this period, Yammer 2.0 was launched and the new version was described as a "Facebook for the Enterprise".

As of June 12, 2012, Yammer has received around US$142 million in funding from venture capital firms such as Charles River Ventures, Founders Fund, Emergence Capital Partners, Goldcrest Investments, and Ron Conway, an angel investor, while the total number of subscribers is close to 8 million.

On June 25, 2012, Microsoft acquired Yammer for US$1.2 billion in cash. Following the acquisition, Microsoft announced that the Yammer team would be incorporated into the Microsoft Office division, but would continue to report to Sacks.

On July 24, 2014, Microsoft announced that Yammer development was being moved into the Office 365 development team, and Sacks announced that he was leaving Microsoft and Yammer.