We have known since the 1980s that islet autoantibodies are specific markers of type 1 diabetes (T1D) that are often present years or even decades before diagnosis. The TrialNet international consortium was established in 2003 with the core aim of preventing T1D. Over 2000 high-risk relatives have been identified, monitored and recruited into prevention trials. Longitudinal analyses have refined our ability to predict T1D, prevent dangerous hyperglycaemia at diagnosis and better understand disease heterogeneity and pathogenesis. In addition, the recent demonstration that abatacept and teplizumab preserve beta-cell function in recently diagnosed T1D has lead to ongoing trials to determine their efficacy in secondary prevention. Increased effort is also being directed toward clarifying the environmental determinants of T1D responsible for the increased incidence of T1D over the last 30 years. Recent highlights include the association between probiotic exposure in infancy and protection from T1D in the US and Europe, and microbiome studies that implicate Bacteroides as a key driver of T1D in Finland. The Enviromental Determinant of Islet Autoimmunity (ENDIA) study is poised to determine the relevance of these and other factors to an at-risk Australian population.