Abstract The rising disease burden of diabetes mellitus globally is a major public health priority, placing unsustainable demands on individuals, their carers, health systems and society. The latest estimates show that there was a global prevalence of 425 million people with diabetes in 2017, which is expected to rise to 629 million by 2045. This is fuelled by the global rise in the prevalence of obesity and unhealthy behaviours including poor diets and physical inactivity; these are in turn promoted by wider societal determinants, including changes in nutrition in a global context (the so-called ‘nutrition transition’). The aetiological classification of diabetes principally separates diabetes mellitus into two main types, type 1 and type 2, with type 2 diabetes accounting for most (>85%) of the total diabetes mellitus prevalence. Both of the common forms of diabetes can lead to multisystem complications of microvascular endpoints, including retinopathy, nephropathy and neuropathy, and macrovascular endpoints, including ischaemic heart disease, stroke and peripheral vascular disease. The aetiology of type 1 diabetes is still incompletely understood. The role of modifiable factors in the causation of type 2 diabetes is better understood, making prevention a realistic public health goal.