Family relationships play an essential role in adolescent development. When studying relationship domains (e.g., quality, conflict, communication), researchers typically rely on adolescents and their parents as informants. However, across research teams, domains, and measurement methods, researchers commonly observe discrepant estimates of family relationships between informants' reports. In this article, we review theoretical models for understanding these discrepant reports, summarize research on how the degree of discrepancy between reports informs our understanding of adolescent development, and highlight directions for research. [This is the advance online version of an article published in "Child Development Perspectives."]