The proposed Yucca Mountain repository license application, prepared by the US Department of Energy, was submitted to the US Nuclear Regulatory Commission in 2008, placing the project in the international lead in terms of potential implementation of permanent geologic disposal of high-level nuclear waste. Volcanic risk assessment is an important component of the license application for Yucca Mountain because the site is located in an area that has experienced sporadic, monogenetic basaltic volcanism for millions of years (Figure 19.1). This chapter summarizes the various issues that come into play in volcanic risk assessment at Yucca Mountain, and how a wide range of observational and theoretical approaches are integrated to support that risk assessment. The chapter is organized around four main themes: (i) definition of an igneous event that might affect the repository and the processes associated with such an event; (ii) estimation of event probability by integrating geology, geophysics and geochemistry of volcanism in the region and the use of expert elicitation; (iii) constraining the consequences of an event via analog and theoretical studies; and (iv) abstraction of the above knowledge and incorporation in probabilistic risk assessment. The focus of the chapter is on the underpinning science and approach that have been developed for the Yucca Mountain effort, which can be translated to other repository or long-term facility assessments in volcanic regions. Risk assessment for the license application is currently under way; therefore we do not provide specific, quantitative values of risk except for one historical example that is provided for illustration purposes only.