After ratifying a human rights treaty, all states are required to incorporate the treaty's standards into domestic law. However, the incorporation of treaty standards varies widely around the world. Why have some states changed their laws to incorporate treaty standards while others have not? I argue that to understand this variation it is necessary to consider how domestic politics affects treaty incorporation. As in other domains of international law, incorporation reflects the strength of rival interest groups in society. I contend that treaty incorporation creates supporters and opponents because human rights treaties can have distributional effects and generate conflict among competing moral values. When groups that oppose incorporation are strong, they can hinder treaty incorporation. I test this argument by examining legislation adopted in Latin America against child labor and child marriage. Making use of two original datasets and over 60 semi-structured interviews with civil society leaders, legislators, and representatives of international organizations in six Latin American countries, I show that groups that oppose human rights treaties can undermine their incorporation. This is important as it suggests a previously unexplored reason for some states' failure to incorporate human rights treaties: governments' response to domestic political pressure. As incorporation is often a first step towards compliance, this dissertation contributes theoretically and empirically to the analysis of the causal mediating steps between treaty ratification and compliance.