The Russell 3000 Index is an equity index based on market capitalization. The index was founded and is based in the United Kingdom, but it is used to track the performance of the 3,000 largest publicly traded US stocks, which account for 98% of the US stock market. The Russell 3000 Index is made up of the Russell 1000 Index for large companies and the Russell 2000 Index for small companies. FTSE Russell, a subsidiary of the London Stock Exchange Group, maintains the index, which was launched on January 1, 1984. (LSEG).