LinkedIn went public a year ahead of Facebook, and Wall Street treated its listing as a test of the whole social media wave. It was the first major American social network to sell shares. Its members kept an online record of their careers and connected with colleagues. Recruiters paid to search that map of the working world. By 2011 LinkedIn had more than 100 million members.

Friends From PayPal

Reid Hoffman, an early PayPal executive, started LinkedIn with a small group of friends from SocialNet and PayPal. They launched it in 2003. The bet was that professionals would put their real names and work histories online if the network got them jobs and deals. LinkedIn made money three ways: recruiting tools, advertising and premium subscriptions. Recruiting became the engine that drove the rest.

Microsoft's Biggest Check

LinkedIn priced its shares at $45 in May 2011 and listed on the New York Stock Exchange. The stock more than doubled on its first day of trading. LinkedIn grew steadily as a public company and bought Lynda.com in 2015. A year later, Microsoft bought LinkedIn for $26.2 billion, its largest purchase up to then. Microsoft kept LinkedIn running as an independent brand.

Cover: Brooklyn Bridge, Henry Ward Ranger. Art Institute of Chicago, public domain. Chosen for a great bridge (connections between people).