VIOO offers representative small-cap exposure in a solid vehicle. VIOO tracks the S&P SmallCap 600 Index (or the S&P 600)a market-cap-weighted index of 600 small-cap US stocks that represent about 3% of the US equity market. The fund isnt exactly neutral, making many mild sector bets and generally leaning slightly away from financials towards industrials. That said, VIOO is still able to provide a solid exposure to small-caps. The index is rebalanced on a quarterly basis.