The U.S. Centers for Disease Control and Prevention (CDC) initiated development of the National Health Security Preparedness Index in 2012 to create a platform for measuring the nation’s progress in preparing for, responding to, and recovering from disasters and other large-scale emergencies that pose risks to health and well-being in the United States. As a measurement tool, the Index is designed to summarize levels of preparedness achieved within individual states and for the nation as a whole. This session summarizes proposed updates to the Index for 2015-16 that are designed to improve the validity and reliability of Index measures and enhance the accuracy and utility of comparisons supported across preparedness domains, across states, and over time.