Undocumented Latinx immigrants experience unique factors prior to migration, during migration, and after migration that shape their health. Our review summarizes the limited but growing literature highlighting how exposure to trauma, immigration enforcement, changes to social networks, and discrimination negatively affect the mental and physical health of undocumented Latinx immigrants. We also discuss how policies and social ties can promote their health. We focus on areas of particular concern, including health care, mental health, and HIV. Future research should use interdisciplinary approaches and intersectional frameworks to understand and address health inequities. Conducting research with undocumented Latinx immigrant communities requires community engagement, assurance of confidentiality, and creative recruitment and retention strategies. Recommendations for public health practice include investing in community health centers and organizations to ensure access to health and social services; presenting results with sufficient contextualization to interpret their generalizability; and advocating for federal-, state-, and local-level policy changes that reduce the negative health consequences associated with being undocumented.