Drawing from Nigrescence Theory (Cross, 1991); Social Identity Theory (Tajfel, 1982); and the Ethnic Identity framework (Umaña-Taylor, Yazedjia, & Bámaca-Gómez, 2004), this mixed method dissertation examined three questions: (1) Are there age-group differences in Oaxaqueño/a-heritage adolescents’ and young adults’ ethnic-racial attitudes and Identity-Salient Experiences (ISE)?; (2) Are there age-group differences in the interrelations among ethnic-racial attitudes, reported discrimination from Mexican peers, self-esteem, and Indigenous self-identification?; and (3) Does ethnic identity buffer the predicted negative relationship between discrimination from Mexican peers and self-esteem? Result indicate small overall age-group differences in ethnic-racial attitudes and ISE, but, compared to young adults, adolescents endorsed higher ethnic-racial Self-Hatred attitudes and lower Multiculturalist Inclusive attitudes. While 72% of participants reported experiencing discrimination from their Mexican peers, only 25% of participants recalled an ISE involving discrimination as formative to their identity. Rather, 63% of adolescents and young adults recalled an ISE involving the cultural practices of the Oaxaqueño community as formative. Adolescents and young adults cited ISEs as helping them identify and explore the cultural and racial markers that define the distinctiveness of the Oaxaqueño and Indigenous culture within the Mexican community. Second, adolescents’, but not young adults’, reported discrimination from their Mexican peers was positively correlated with their Miseducation and Self-Hatred attitudes. Only ethnic-racial Self-Hatred attitudes were negatively related to adolescents’ and young adults’ self-esteem. Among Oaxaqueño/a-Indigenous youth, those who self-identified as Indigenous reported more discrimination from Mexican peers than those who did not self-identify as Indigenous. Third, there was no evidence that ethnic identity buffered the negative effect of discrimination. Findings lend support for adolescence as a time when Oaxaqueño/a-heritage youth are particularly attuned to discrimination from their Mexican peers. The findings indicate that while discrimination may not be formative to adolescents’ identity as Oaxaqueño/a, they were related to their learned and internalized stereotypes about the Oaxaqueño community. Findings also reveal how ethnicity and race together shape Oaxaqueño/a-heritage youths’ sense of belonging as Mexican, Oaxaqueño/a, and Indigenous in adolescence and young adulthood. Finally, implications for the three theoretical models framing the study are discussed.