In the 1990s, several liberal welfare regimes (LWRs) introduced child tax credits (CTCs) aimed at reducing child poverty. While in other countries these tax credits were refundable, the United States alone introduced a nonrefundable CTC. As a result, the United States was the only country in which poor and working-class families were paradoxically excluded from these new benefits. A comparative analysis of Canada and the United States shows that American exceptionalism resulted from the cultural legacy of distinct public policies. We argue that policy changes in the 1940s institutionalized different "logics of appropriateness" that later constrained policymakers in the 1990s. Specifically, the introduction of family allowances in Canada and other LWR countries naturalized a logic of income supplementation in which families could legitimately receive cash benefits without the stigma of "welfare. " Lacking this policy legacy, American attempts to introduce a refundable CTC were quickly derailed by policymakers who saw it as equivalent to welfare. Instead, they introduced a narrow, nonrefundable CTC under the alternative logic of "tax relief, " even though this meant excluding the lowest-income families. The cultural legacy of past policies can explain American exceptionalism not only with regard to CTCs but to other social policies as well.