Now that LinkedIn has stock is trading publicly, , you can buy and sell shares of the company on the New York Stock Exchange. But its shares have traded before privately among wealthy individuals and other accredited investors on secondary markets such as SecondMarket. The chart above shows the price history of LinkedIn’s stock between April, 2010 and March 2011 on SecondMarket. On SecondMarket, LinkedIn's value per share in April, 2010 came in at $14.50 and steadily rose to $35 by March, 2011. Yesterday, LinkedIn priced its IPO at $45 per share on the NYSE, giving the company a valuation of $4.5 billion. Today, the company began trading publicly at $83.00 per share, an 84 percent increase from $45 per share. That’s a $7.8 billion market cap. And shares have been trading as high as $122 per share today.