While many investors think of the S&P 500 (SNPINDEX:^GSPC) as a static index that rarely changes, the reality is that it's in a constant state of flux. This year alone, it changed out nearly 20 component companies, leaving stocks like Teradyne (NYSE:TER) and JDS Uniphase (NASDAQ:VIAV) in the lurch. In the video below, Fool contributor John Maxfield discusses which other stocks got kicked off the index -- for a full list, plus the date of and reason for removal, see the table beneath the video.

Date

Removed

Replaced By

Reason for Removal

April 30

MetroPCS Communications

Regeneron Pharmaceuticals

Merged with T-Mobile USA, dropping public float below 50% threshold

May 8

Coventry Health Care

The Macerich Co.

Acquired by Aetna

May 23

Dean Foods

Kansas City Southern

Equity interest in WhiteWave Foods spun off making Dean Foods "more representatives of the midcap market space"

June 6

H.J. Heinz Co.

General Motors

Acquired by Berkshire Hathaway

June 21

First Horizon National

Zoetis

Insufficient market capitalization

June 28

Apollo Education Group

News Corp

Insufficient market capitalization

July 8

Sprint Nextel

Nielsen Holding

Capital infusion by Japan's SoftBank dropped public float below 50% threshold

Sept. 10

BMC Software

Delta Air Lines

Acquired by private equity firm Bain Capital

Sept. 20

Advanced Micro Devices

Vertex Pharmaceuticals

Insufficient market capitalization

Sept. 20

Science Applications International Corp.

Ametek

Split into two companies: SAIC and Leidos Holdings

Oct. 28

Dell

Transocean

Taken private by founder-led buyout

Nov. 1

NYSE Euronext

Michael Kors

Acquired by Intercontinental Exchange

Nov. 29

J.C. Penney

Allegion

Insufficient market capitalization

Dec. 9

Molex

General Growth Properties

Acquired by privately held Koch Industries

Dec. 20

Abercrombie & Fitch

Alliance Data Systems

Insufficient market capitalization

Dec. 20

JDS Uniphase

Mohawk Industries

Insufficient market capitalization

Dec. 20

Teradyne

Facebook

Insufficient market capitalization

Source: S&P Dow Jones Indices.

John Maxfield has no position in any stocks mentioned, and neither does The Motley Fool. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.