VIX is the ticker symbol for the Chicago Board Options Exchange Volatility Index, a popular measure of the implied volatility of S&P 500 index options. A high value corresponds to a more volatile market and therefore more costly options, which can be used to defray risk from this volatility by selling options. Often referred to as the fear index, it represents one measure of the market's expectation of volatility over the next 30 day period.

The volatility index is an index which measures expectations of volatility, or fluctuations in price, of the S&P 500 index. Higher values for the volatility index indicate that investors expect the value of the S&P 500 to fluctuate wildly - up, down, or both - in the next 30 days.

The index, commonly known by its ticker VIX, is also known as the "fear index" because a high VIX represents uncertainty about future prices. The index is calculated using the price of near-term options on S&P 500 index.^[1] Because the value of an option is closely linked to the expected volatility of its underlying security, options prices can be a useful indicator of investors' expectations of volatility.

The VIX hit its historic high of 89.53 on October 24, 2008 on concerns about the 2008 Financial Crisis. Prior to this crisis, the VIX had peaked at 38 on August 8, 2002.

There is no security that realizes the VIX's "return" (like ETFs for regular indices). However, VIX-based futures contracts and options exist for professional investors. In January 2009, iPath launched two securities (VXX and VXZ) that track VIX futures rather than the VIX itself. These securities allow retail investors to speculate on the VIX.^[2]

There are other volatility indexes which track expected volatility on other indices: VXD is used as an indicator of expected volatility of the Dow Jones Industrial Average and VXN is used for the NASDAQ 100 index.