Explore gravitational wave detection theory in this comprehensive lecture delivered by Barak Zackay from the Weizmann Institute as part of the Prospects in Theoretical Physics 2025 series at the Institute for Advanced Study. Delve into the theoretical foundations underlying gravitational wave detection methods and gain insights into the cutting-edge research shaping our understanding of these cosmic phenomena. Examine the mathematical frameworks, signal processing techniques, and theoretical models that enable scientists to identify and analyze gravitational waves from astronomical events. Learn about the challenges and innovations in detection theory that continue to advance the field of gravitational wave astronomy and expand our ability to observe the universe through these ripples in spacetime.