Fire has, does, and will shape forest structure, composition, and biodi-versity. In this book, we introduce the driving forces, historical patterns, and future management challenges of fire in forested ecoregions across the continental USA. Climate warming and decades of fire suppression or exclusion have altered historical fire regimes and threaten diversity of fire-adapted forest vegetation into the future. Historical fire regimes ranged from frequent, low-severity fires in some ecosystems to infrequent, high-severity fires in others. They were driven by interactions among climate, drought cycles, topography and soils, fuel type and accumulation, and ignition frequencies by lightning; and increasingly by humans as Native American populations expanded in many ecoregions. Fires burned across large landscapes in ecosystems where fuels were continuous, such as pine-savanna ecosystems of the Southeastern Coastal Plain or ponderosa pine forests of the Southwest. Today, decades of fire exclusion have led to divergent outcomes: succession toward forests less apt to burn (mesophication), or more frequent or higher-severity wild-fires. Management of fire toward future forests will require careful definition of desired future and references conditions establishing priorities, and working across agency boundaries to implement prescriptions.