Obesity is one of the greatest public health challenges of the 21st century. Affecting over half a billion people worldwide, it increases the risk of stroke, ischaemic heart disease, diabetes, many cancers, depression and complications in pregnancy. Bariatric surgery is currently the only effective treatment available but is associated with significant risks of mortality and long-term complications. New and innovative treatments are thus required.The signals to and from the gut during eating and digestion are passed through the vagus nerve. Despite this, our knowledge of vagus nerve function comes from studies in which the nerve is cut. This fails to provide any impression of the complex signal received by appetite centres in the brain.We propose to use obesity as a paradigm for development of a new generation of neural interface that will combine novel electrode materials, structures and sensing modalities with ultra-low power electronic neural recording, analysis, stimulation and wireless communication. Several steps beyond state-of-the-art, this will allow, for the first time, detailed study of the entirety of vagus nerve function. We will develop neural stimulation that mimics the response of the vagus nerve to ingestion of food, thus providing a new treatment for obesity.The synergy between our groups will thus combine complementary interests to develop an innovative technological solution for a major public health crisis. The sensing capability will deliver, for the first time, real-time and long-term recordings, providing new insights into peripheral nerve activity. The impact will thus extend beyond appetite and the vagus to many other neurally regulated processes and diseases.