Approximately 90% of the American population has grown up with at least one sibling, and this is often the longest lasting relationship most people will have in their lives (Milevsky, 2011). Yet, the sibling literature is still burgeoning and significant gaps exist regarding ways that the sibling subsystem may be affected by intrafamilial abuse. The current article examines sibling roles, relationships, and functions through the lens of family systems theory and gives an overview of research conducted on siblings, with special focus on studies about siblings in abusive families. We then propose a theoretical typology of sibling subsystems that may develop in an abusive family system. Implications for research, theory, and clinical practice are discussed.