We explore after-hours trading (AHT) in U.S. equity markets. We collect a large set of news releases during AHT and document their effect on AHT activity and market quality. There are three major triggers of AHT. After-hours corporate news catches the attention of retail participants. We use a machine learning method on retail trades to construct a new measure of retail trading activity during AHT. Zero-commission platforms facilitate a reaction of retail traders to positive after-hours corporate news that increases after-hours trades and return volatility. Insider sales are more likely to be announced after markets close allowing faster correction of company overvaluations. Index rebalancing and reconstitutions during AHT lead to large liquidity-driven trades contributing to the negative CAPM slope.