A limit-order market enables an early investor to trade with a late investor. But, public news in the interarrival
period creates adverse-selection cost and hampers trade. A high frequency trader (HFT) might restore trade
through its unique ability to quickly update its quote on news arrival. But, HFT entry might in itself worsen
adverse selection if speed is used to adversely select investors’ quotes. This paper studies HFT entry both
theoretically and empirically. The entry of an HFT-friendly new market is used as an instrument. Middlemen
arrival coincides with a 29% reduction in the bid-ask spread and a 13% drop in volume.