The VIX Index tracks the amount of defensive options being purchased on the Chicago Board of Options Exchange (CBOE). This represents the amount of insurance investors are seeking to protect their portfolios against downside risk. As volitity and downside fear increases these indexes increase in value.
iPath is set to issue two new ETNs covering iPath S&P 500 VIX Short-Term Futures and the iPath S&P 500 VIX Mid-Term Futures ETNs . Read Murray Coleman's article on the topic here.