High-frequency traders (HFTs) accounted for roughly forty percent of trading volume on the NASDAQ Stock Market in 2009, but there is little evidence on the type of information these investors trade on. This study tests the hypothesis that HFTs anticipate and trade ahead of other investors' order flow. I find that HFTs' aggressive purchases predict future aggressive buying by non-HFTs, and their aggressive sales predict future aggressive selling by non-HFTs. The positive correlation between trading by HFTs and future trading by other investors is robust to the exclusion of trading around news releases, indicating the effect is not driven by HFTs reacting to news announcements faster than other investors. The effects are stronger in the morning and on high volume days. There are also persistent differences among HFTs in the tendency of their trades to predict future order flow. These findings have implications for the speed at which prices adjust to new information, incentives to acquire information, and the price impact of traditional asset managers' trades. / text