Once celebrated for their innovative design, important modern buildings around the world are now at risk, endangered due to neglect, inappropriate alterations, deterioration, and, often, demolition. For the last two decades, the World Monuments Watch has called attention to threatened modern sites as a key issue in the field of heritage preservation. This presentation will offer an overview of the modern sites featured on the Watch since 1996, ranging from the iconic, including Alvar Aalto’s Viipuri Library and Philip Johnson’s New York State Pavilion, to the less widely known, including Hilario Candela’s Miami Marine Stadium and Vann Molyvann’s National Sports Complex. Examples of successes, challenges, and irreplaceable losses will be shared.