This document provides a summary of the Scientific Workshop to Inform EPA's Response to National Academy of Science Comments on the Health Effects of Dioxin in EPA's 2003 Dioxin Reassessment. The U.S. Environmental Protection Agency (U.S. EPA) and Argonne National Laboratories (ANL), through an Inter-Agency agreement with the U.S. Department of Energy, convened this scientific workshop (Dioxin Workshop) on February 18-20, 2009, in Cincinnati, Ohio. The goals of theDioxin Workshop were to identify and address issues related to the dose-response assessment of 2,3,7,8-tetrachlor odibenzo-p-dioxin (TCDD). This report summarizes the discussions and conclusions from this workshop. Previously, at the request of the U.S. EPA, the National Academy of Sciences (NAS) prepared a report, Health Risks from Dioxin and Related Compounds: Evaluation of the EPA Reassessment (NAS, 2006), which made a number of recommendations to improve the U.S. EPA's risk assessment for TCDD (U.S. EPA, 2003). The 3-day Dioxin Workshop was convened specifically to ensure that the U.S. EPA's response to the NAS recommendations focuses on the key issues and reflects the most meaningful science.