The Russell 2000 Index is a stock market index that measures the performance of 2,000 small-cap companies in the United States. It is part of the larger Russell 3000 Index, which includes the 3,000 largest U.S. stocks. The index is widely used by investors to gauge the performance of small-cap stocks and to assess the overall health of the small-cap segment of the market. Investors often use the Russell 2000 as a benchmark for small-cap investments. The index is reconstituted annually, meaning it is updated to reflect changes in the market, such as new companies entering the small-cap space or existing companies growing beyond the small-cap threshold.