ShakeCast is a US Geological Survey (USGS) software application that automatically retrieves ShakeMap shaking estimates and performs analyses using fragility functions for buildings and lifelines. The ShakeCast system aims to identify which facilities or lifeline segments are most likely impacted by an earthquake—and thus which ones should be prioritized for inspection and response—and sends notifications to responders in the minutes after an event. By focusing inspection efforts on the most damage-susceptible facilities in the severely shaken areas, ShakeCast can improve critical lifeline inspection prioritization and reduce response time in the aftermath of a significant earthquake. Overviews and technical specifications of the ShakeCast system and software have been presented at earlier conferences; here we discuss ShakeCast users and their response protocols to provide further insight into the use of the ShakeCast system. We focus on case histories of ShakeCast users who are responsible for monitoring and response for critical infrastructure. We emphasize the inventory, fragility, and notification issues pertinent to these users, their efforts in developing protocols for post-earthquake inspections, and response.