The Advanced National Seismic System (ANSS) is an effort to modernize, expand, and integrate earthquake monitoring and notification in the United States. The ANSS grew out of a requirement to the U.S. Geological Survey (USGS) by Congress to assess seismic monitoring nationwide. The resulting ANSS plan defines earthquake monitoring needs on national, regional, and urban scales with 100, 1,500, and 6,000 new instruments or seismic stations at each scale, respectively. A national seismic network provides nationwide coverage at about magnitude 4.0 or higher. Dense regional networks in areas of high to moderate seismicity provide details of the seismicity, at about the magnitude 2.0 level, associated with active tectonic structures. Seismic instruments in urban areas provide the data needed for rapid, quantitative assessments of the geographic distribution and severity of ground shaking immediately after a nearby earthquake. Emergency officials and infrastructure managers use these assessments to direct emergency response and to minimize losses and disruption. Urban instruments also provide the data needed for earthquake-resistant design and construction. Implementation of the ANSS has begun at a modest level in all seismically active regions of the country. The guiding concept is based on regional planning and implementation with national oversight and design. The intent of the ANSS concept is not only to expand the number of instruments and the volume of relevant data, but also to integrate seismic data recording and processing facilities into a unified and robust national earthquake monitoring and notification system.