The current study examines the role of economic strain as a moderator of the microsocial processes influencing younger siblings’ delinquency (externalizing behavior and substance use) in a longitudinal design. The younger siblings (122 younger brothers and 122 younger sisters) were from 244 families with same-sex biological siblings. Structural equation modeling was utilized to examine a process model whereby mothers’ harsh/inconsistent parenting and older sibling delinquency influence younger siblings’ delinquent behavior via sibling aggression and delinquent peer affiliation. Findings suggest that indirect mechanisms vary as a function of economic strain, with sibling aggression having a stronger, more detrimental effect on adolescent delinquency in economically strained families. Data suggest that familial economic conditions contextualize the relative roles of parenting, sibling, and peer processes in the transmission of risk to adolescent delinquency.