Billion-dollar companies have been part of the U.S. economy for more than a century. Trillion-dollar companies, however, are a more recent development. Although Apple (AAPL -1.66%) is often considered to be the first publicly traded company to reach $1 trillion in market capitalization, it's neither the first nor the last to reach a four-comma valuation. Read on to learn more about the trillion-dollar club's history, as well as its past, present, and potential future members.
