The Russell Microcap Index measures the performance of the microcap segment of the U.S. equity market. It makes up less than 3% of the U.S. equity market. It includes 1,000 of the smallest securities in the Russell 2000 Index based on a combination of their market cap and current index membership and it also includes up to the next 1,000 stocks. As of 31 December 2016, the weighted average market capitalization for a company in the index was $535 million; the median market cap was $228 million. The market cap of the largest company in the index was $3.6 billion.
The index, which was launched on June 1, 2005, is maintained by FTSE Russell, a subsidiary of the London Stock Exchange Group. Its ticker symbol is ^RUMIC.