In this lecture divided into 9 chapters, Dr. Cryan presentes the studies involving animal models, early-life microbiota manipulations, and probiotic administration in adulthood. Their research has shown that gut microbiota is essential for normal stress, antidepressant, and anxiety responses. Dr. Cryan will discuss his work as well as the concept of critical windows of time early in life when the effects of microbiota on brain and behavior appear to be more potent. Manipulation of the microbiota in early life by cesarean delivery, antibiotics, or stress leads to long-lasting effects on brain and behavior. Dr. Cryan will also discuss how specific modulation of the enteric microbiota through diet may be a useful "psychobiotic"-based strategy for both stress-related and neurodevelopmental disorders ranging from depression to autism.