People with intellectual disability (ID) are excluded from life experiences that people perceived as nondisabled take for granted. This chapter provides a primer for the eye movement desensitization and reprocessing (EMDR) therapist interested in treating posttraumatic stress in people with ID. Clients with ID treated by the authors suffered repeated and varied negative life experiences that kindled into a cluster of symptoms now widely understood as complex trauma. People with ID and psychiatric disorders are often undiagnosed because the symptoms look different from standard symptom presentation. Psychiatric symptoms are often expressed as behavior. People with ID suffered population level, institutionalized abuse that persisted from the late 19th century into the 1970s. That abuse included medical experimentation and forced sterilization. The chapter discusses the cultural construction of ID to support clinicians in recognizing environmental challenges to trauma treatment consequent to culturally mediated attitudes and beliefs.