Tesla Will Join S&P 500 In December

Tesla will join the S&P 500 on December 21, S&P Dow Jones Indices announced Monday.

With a market cap of nearly $400 billion, Tesla joins as one of the 10 most valuable companies in the index.

S&P Global did not say which company Tesla will replace later this year.

Shares of the electric-vehicle manufacturer jumped more than 13% on the news in after-hours trading.

The S&P 500 is an index of 500 large US companies, says Business Insider.

It is seen as one of the most important gauges of the success of America's largest publicly-traded firms.