The theory of historical trauma was developed to explain the current problems facing many Native Americans. This theory purports that some Native Americans are experiencing historical loss symptoms (e.g., depression, substance dependence, diabetes, dysfunctional parenting, unemployment) as a result of the cross-generational transmission of trauma from historical losses (e.g., loss of population, land, and culture). However, there has been skepticism by mental health professionals about the validity of this concept. The purpose of this article is to systematically examine the theoretical underpinnings of historical trauma among Native Americans. The author seeks to add clarity to this theory to assist professional counselors in understanding how traumas that occurred decades ago continue to impact Native American clients today.