The world is facing a health crisis due to increasing rates of obesity and diabetes, and the consequences will accumulate over the coming decades. Simultaneously, climate change is accelerating and is already having devastating effects; these changes will undermine the ability to produce adequate healthy food for the world’s growing population. A rapid shift away from fossil fuels to green energy is essential, and adoption of diets that largely plant-based must play an important role; this will have major benefits for human and planetary health including a 25 to 30% decrease in premature death rate. In this lecture, Harvard physician and epidemiologist Dr. Walter Willett will showcase how the traditional diets of the Mediterranean region have been shown to promote excellent health and have been sustainable over thousands of years. Dr. Willett is a physician and epidemiologist and Professor of Epidemiology and Nutrition at the Harvard T.H. Chan School of Public Health. He served as Chair of the Department of Nutrition at Harvard for 25 years.