Salt marshes are vitally important coastal ecosystems that filter water, buffer against storm erosion, and provide essential nursery habitat for important fishery species. Long thought to be resistant to ecological perturbations, salt marshes are now known to be highly sensitive indicators of environmental change and impacts. This state—of—the—science volume details how humans have modified salt marshes around the world and why these critical habitats desperately need protection. It also offers clear recommendations about what should be done to remediate current threats and restore the structure and function of salt marsh ecosystems.