We show that an increase in passive exchange-traded fund (ETF) ownership leads to stronger and more persistent return reversals. Exploiting exogenous changes due to index reconstitutions, we further show that more passive ownership causes higher bid-ask spreads, more exposure to aggregate liquidity shocks, more idiosyncratic volatility, and higher tail risk. We examine potential drivers of these results and show that higher passive ETF ownership reduces the importance of firm-specific information for returns but increases the importance of transitory noise and a firm's exposure to market-wide sentiment shocks.