Delve into the fascinating world of gravitational theories in this comprehensive lecture by Shinji Mukohyama from YITP, Kyoto University. Explore the foundations of modified gravity and gain insights into cutting-edge research in the field. Over the course of two and a half hours, examine the fundamental concepts, mathematical frameworks, and experimental evidence that shape our understanding of gravity beyond Einstein's General Relativity. Engage with complex ideas presented by a renowned expert, and discover how these theories impact our perception of the universe and its underlying physical laws.