The National Estuarine Research Reserve System (NERRS) is an integrated network of 29 protected and coordinated estuarine reserve sites in 23 states and one territory (Puerto Rico) covering more than 525,000 ha of estuarine habitat, adjoining wetlands, and uplands that encompass 19 biogeographical regions along the Atlantic, Gulf of Mexico, and Pacific coasts, as well as the Caribbean Sea and Great Lakes. NERRS is an ecosystem-based research and monitoring network of sites serving as platforms to develop quantitative databases of value to coastal management programs in identifying and tracking short-term variability and long-term changes in the integrity and biodiversity of estuarine systems nationwide due to natural perturbations and anthropogenic disturbances. The reserve sites also play a vital role in assessing coastal issues of local, regional, and national significance for the purpose of sustaining estuarine systems and coastal lands, such as evaluating their responses to climate change and other major stressors to inform coastal decision-making and public awareness for the protection and resilience of natural resources and coastal communities. Over the past four decades, NERRS sites have collected large volumes of research and monitoring data of great utility in characterizing estuarine environments and addressing an array of resource-management concerns, including degraded water quality, loss and alteration of essential habitat, impacted fisheries, invasive species, and conservation.