In this study, we extend the Chicago Board Options Exchange volatility index, VIX, from 30-day to any arbitrary time-to-maturity, and study the term structure of VIX. We propose new concepts of instantaneous and long-term squared VIXs as the limits at the short and long ends of the term structure respectively. Modeling the volatility process with instantaneous and long-term squared VIXs, we establish a parsimonious approach to capture information contained in the term structure of VIX. Our study provides an efficient setup to further study the pricing of VIX derivatives and their relation with S&P 500 options.