The S&P MidCap 400 Index, more commonly known as the S&P 400, is a stock market index from S&P Dow Jones Indices. The index serves as a barometer for the U.S. mid-cap equities sector and is the most widely followed mid-cap index in existence. To be included in the index, a stock must have a total market capitalization that ranges from $1.4 billion to $5.9 billion at the time of addition to the index. As of 29 December 2017, the median market cap was almost $4.1 billion with the market cap of the largest company in the index at more than $13.1 billion and the smallest company at $626 million. The index's market cap covers nearly 7 percent of the total US stock market. The index was launched on June 19, 1991.
It has set a series of all-time highs since the Federal Reserve announced its third round of recent quantitative easing in mid-September 2012. At the weekly and monthly close of November 30, 2012, the index settled at the 1,000 point mark, and it has continued to rise in early 2013, setting new records above 1,200 by mid-May.