This special issue for the Journal of Endocrinology celebrates the 30th anniversary of David Barker's seminal findings that led to the scientific field of the Developmental Origins of Health and Disease (DOHaD). In 1989, Barker and colleagues reported that low birth weight and weight at one year, proxies for fetal growth restriction, were related to an individual's risk for developing hypertension and cardiovascular heart disease. Barker's initial epidemiological studies also demonstrated that low birth weight was predictive of later glucose intolerance, Type 2 Diabetes, and other metabolic-related diseases. As the developmental origins concept developed, the number of epidemiological studies continued to expand globally, consistently demonstrating the higher risk of developing chronic degenerative diseases if one was born small. In this thematic issue on the early origins of disease, there are a series of review articles and research papers that capture the impact of early events on endocrine systems, as major mechanisms underlying Barker's original observations. Importantly, over the past 30 years as the DOHaD concept has become widely accepted, we have seen it applied to an ever expanding breadth of human health problems. This expansion is evidenced by the growth of new model systems and establishment of new causal relationships in neuroendocrinology, reproductive systems, obesity, and behavior. The importance the DOHaD concept, its continued evolution, and new underlying mechanism are captured in the articles of this issue dedicated to Professor Barker's legacy.