Clare Llewellyn, PhD, is a chartered psychologist and associate professor of obesity at University College London, where she leads the Obesity Research Group and the Gemini twin study. In 2011 she completed her PhD at UCL on the nature and nurture of eating behavior and weight in early life and she has a long-standing fascination with the topic, which probably stems from having been a notoriously fussy eater as a child. A decade ago she helped establish Gemini, the largest twin study ever set up to explore the nature and nurture of eating behavior from the beginning of life. She has published nearly 100 scientific papers, articles and book chapters on this topic and has given over sixty invited talks worldwide at international organizations, such as the American Dietetic Association, the UK Royal Society of Medicine and the European Society for Paediatric Gastroenterology Hepatology and Nutrition. She lives in London with her partner, Andy.