The Russell Top 50 Index also known as the Russell Top 50 Mega Cap is a stock market index that measures the performance of the largest companies in the Russell 3000 Index. It includes approximately 50 of the largest securities based on a combination of their market cap and current index membership and represents approximately 40% of the total market capitalization of the Russell 3000. The index, which was launched on January 1, 2005, is maintained by FTSE Russell, a subsidiary of the London Stock Exchange Group. Its ticker symbol is ^RU50. Wikipedia