Volcanic eruptions are common, with more than 50 volcanic eruptions in the United States alone in the past 31 years. These eruptions can have devastating economic and social consequences, even at great distances from the volcano. Fortunately many eruptions are preceded by unrest that can be detected using ground, airborne, and spaceborne instruments. Data from these instruments, combined with basic understanding of how volcanoes work, form the basis for forecasting eruptions?where, when, how big, how long, and the consequences. Accurate forecasts of the likelihood and magnitude of an eruption in a specified timeframe are rooted in a scientific understanding of the processes that govern the storage, ascent, and eruption of magma. Yet our understanding of volcanic systems is incomplete and biased by the limited number of volcanoes and eruption styles observed with advanced instrumentation. Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing identifies key science questions, research and observation priorities, and approaches for building a volcano science community capable of tackling them. This report presents goals for making major advances in volcano science. Table of Contents Front Matter Overview Summary 1 Introduction 2 How Do Volcanoes Work? 3 Forecasting Eruptions 4 How Do Earth Systems Interact with Eruptions? 5 Strengthening Volcano Science 6 Grand Challenges in Volcano Science References Appendix A: Volcano Databases Appendix B: Workshop Participants Appendix C: Biographical Sketches of Committee Members Appendix D: Acronyms and Abbreviations