In 2016, the U.S. Department of Homeland Security (DHS), Office of PolicyStrategy, Plans, Analysis, and Risk (SPAR), asked the RAND National Defense Research Institute to design and implement a risk identification and characterization of natural and manmade threats and hazards to identify the greatest risks to homeland security and support prioritization of DHS mission elements as part of DHS strategic planning processes. This report describes the risk assessment methodology RAND researchers developed to address these goals. It also presents summary sheets of threats and hazards to inform discussion of DHS risk management priorities, which are included in an accompanying For Official Use Only volume. A separate policy-oriented report will be issued by the DHS Office of Policy to present key findings about the risks from homeland security threats and hazards and the priorities for managing them. This research was sponsored by SPAR and conducted within the RAND Homeland Security and Defense Center, a joint center of RAND Justice, Infrastructure, and Environment and the RAND National Defense Research Institute (NDRI), a federally funded research and development center sponsored by the Office of the Secretary of Defense, the Joint Staff, the Unified Combatant Commands, the Navy, the Marine Corps, the defense agencies, and the defense Intelligence Community.