Using a population-based survey experiment, this study evaluates the role of in-group favoritism in influencing American attitudes toward international trade. By systematically altering which countries gain or lose from a given trade policy (Americans and/or people in trading partner countries), we vary the role that in-group favoritism should play in influencing preferences. Our results provide evidence of two distinct forms of in-group favoritism. The first, and least surprising, is that Americans value the well-being of other Americans more than that of people outside their own country. Rather than maximize total gains, Americans choose policies that maximize in-group well-being. This tendency is exacerbated by a sense of national superiority; Americans favor their national in-group to a greater extent if they perceive Americans to be more deserving. Second, high levels of perceived intergroup competition lead some Americans to prefer trade policies that benefit the in-group and hurt the out-group over policies that help both their own country and the trading partner country. For a policy to elicit support, it is important not only that the US benefits, but also that the trading partner country loses so that the US achieves a greater relative advantage. We discuss the implications of these findings for understanding bipartisan public opposition to trade.