While the Russell 5000 Index does not exist, the Russell 3000, 2000 and 1000 Indexes do, according to Russell Indexes. The Russell 3000 Index monitors the 3,000 largest U.S. companies, and the Russell 2000 Index is a subset of the 3000 Index that measures about 2,000 of the smallest securities.
The Russell 1000 Indexes are a subset of the 3000 Index that measure the largest securities, says Investopedia. The Russell 2000 and 1000 Indexes' securities are judged by their market cap and current index membership, according to Russell Indexes. All three indexes are redone annually to make sure only stocks that meet market cap and size requirements are included.