[Using a variety of different definitions of "neutrality," this study presents significant evidence against the neutrality to market risk of hedge funds in a range of style categories. I generalize standard definitions of "market neutrality," and propose five different neutrality concepts. I suggest statistical tests for each neutrality concept, and apply these tests to a database of monthly returns on 1423 hedge funds from five style categories. For the "market neutral" style, approximately one-quarter of the funds exhibit significant exposure to market risk; this proportion is statistically significantly different from zero, but less than the proportion of significant exposures for other hedge fund styles.]

One can consider the concept of market neutrality for hedge funds as having breadth and depth: "breadth" reects the number of market risks to which a fund is neutral, while "depth" reects the "completeness" of the neutrality of the fund to market risks. We focus on market neutrality depth, and propose ve different neutrality concepts. "Mean neutrality" nests the standard correlation-based denition of neutrality. "Variance neutrality", "Value-at-Risk neutrality" and "tail neutrality" all relate to the neutrality of the risk of the hedge fund to market risks. Finally, "complete neutrality" corresponds to independence of the fund to market risks. We suggest statistical tests for each neutrality concept, and apply the tests to a combined database of monthly "market neutral" hedge fund returns from the HFR and TASS hedge fund databases. We nd that around one-quarter of these funds exhibit some signicant exposure to market risk.