What does it really mean to be "undocumented," particularly in the contemporary United States? Political philosophers, immigration policy makers, and others have tended to define the term "undocumented migrant" legalistically - that is, in terms of lacking legal authorization to live and work in one's current country of residence. In Socially Undocumented, Reed-Sandoval challenges this "legalistic understanding" by arguing that being socially undocumented is to possess a real, visible, and embodied social identity that does not always track one's legal status. She further argues that achieving immigration justice in the U.S. (and elsewhere) requires a philosophical understanding of the racialized, class-based, and gendered components of socially undocumented identity and oppression. Socially Undocumented offers a new vision of immigration justice by integrating a descriptive and phenomenological account of socially undocumented identity with a normative and political account of how the oppression with which it is associated ought to be dealt with as a matter of social justice. It also addresses concrete ethical challenges such as the question of whether open borders are morally required, the militarization of the Mexico-U.S. border, the perilous journey that many migrants undertake to get to the United States, the difficult experiences of the women who cross U.S. borders seeking prenatal care while pregnant, and more.