The current study draws from literature on Multiracial ethnic-racial identity development processes and utilizes logistic regression models to identify what factors inform ethnic-racial self-categorization choices when confronted with a monoracial paradigm of race in a sample of Biracial high school students. Separate logistic regression models analyzed how family ethnic-racial socialization, phenotype, friend groups, and experiences with discrimination are associated with the racial category for Biracial White, Asian, Black, Native American, and Latinx youth, respectively, when asked to choose just one racial background. Results suggest that the associations of family ethnic-racial socialization, experiences with discrimination, and skin color with self-categorization vary in directionality and strength for different groups of Biracial adolescents. However, adolescents with a greater proportion of friends in a given ethnic-racial group were more likely to self-categorize with that respective ethnic-racial group across all models. These findings provide a nuanced understanding of how Biracial youth draw on various aspects of their lived experiences when confronting monoracism.