Background: Binge drinking peaks in emerging adulthood and is associated with a myriad of negative consequences. Research indicates that social network members have a significant influence on binge drinking. In particular, theory suggests that drinking habits of romantic partners and peers have a stronger influence on emerging-adult binge drinking than do drinking habits of siblings and parents. We investigated the relative influences of siblings, parents, romantic partners, and peers on emerging adults’ binge drinking using a multisource design and a robust measure of binge drinking. We hypothesized peer and romantic partner binge drinking would more strongly predict emerging-adult (egos) binge drinking than would parent and sibling binge drinking. Methods: We recruited 321 participants (egos) aged 17–25 years, alongside 882 members of their social network (alters). Egos and alters completed self-report measures of binge drinking (frequency, quantity, and self-perception). Results: Structural equation modeling revealed that the direct positive effect from romantic partner binge drinking to ego binge drinking was significant. In contrast, the direct effects from peer, parent, and sibling binge drinking to ego binge drinking were nonsignificant. Conclusion: In emerging adulthood, romantic partners appear to have the strongest association with ego binge drinking.