Political scientists have long viewed values as a source of constraint in political belief systems. More recently, scholars have argued that values—particularly moral values—contribute to polarization. Yet, there is little direct and systematic research on which values are perceived as moral values. We examine 21 values, including Schwartz’s values, political values, and moral foundations. Drawing on a broad literature on cooperation, we first develop theoretical expectations for the extent of value moralization both between and within value systems. We next argue that this moralization matters because it intensifies the effects of value disagreement on social polarization. Using a probability-based survey of the US and an embedded conjoint experiment, we find substantial variation in moralization across values, and that highly moralized values are more polarizing. Our research brings together competing literatures on values and shows how moral values differentially shape polarization.