This study investigated whether the patterns of direct association, and of gene-environment interaction (GxE), between family variables (i.e., parenting, family conflict, and attitudinal familism) and youth externalizing behaviors differed across racial/ethnic groups. The sample was composed of 772 twin pairs from the Adolescent Brain Development Study (ABCD) and analyses were run on three racial/ethnic groups (White [n=1023], Black/African American [n=220], Hispanic [n=152]; Mage=10.14 years). Youth reports of parental warmth, parental monitoring, family conflict, parent-reported attitudinal familism, and parent reports of youth externalizing behaviors were collected at baseline when children were 10 years old. Regression analyses tested the direct association between the family variables and youth externalizing behaviors, and moderated heritability models tested for GxE. Family conflict was associated with more externalizing behaviors for White youth, and parental warmth was associated with fewer externalizing behaviors for Hispanic youth. Parental attitudinal familism composite and familism support were associated with fewer externalizing behaviors for Black youth but more externalizing behaviors for Hispanic youth. We found no effects for parental monitoring, familism obligations, and familism referent on youth externalizing behaviors. Additive genetic and non-shared environmental influences explained the variance in youth externalizing behaviors across all groups. For White youth, parental warmth, parental monitoring, and familism support moderated additive genetic (A), shared-environmental (C), and non-shared environmental (E) influences on externalizing behaviors, and familism obligations moderated C and E influences. Results from exploratory moderated heritability analyses conducted for the Black/African American and Hispanic samples are discussed. Altogether, these findings highlight the multiple avenues through which the family context can impact the development of youth externalizing behaviors, and reinforce the need to examine how these relations differ across racial/ethnic groups.