This guideline covers how to identify adults at high risk of type 2 diabetes. It aims to remind practitioners that age is no barrier to being at high risk of, or developing, the condition. It also aims to help them provide those at high risk with an effective and appropriate intensive lifestyle-change programme to prevent or delay the onset of type 2 diabetes. The recommendations in this guideline can be used alongside the NHS Health Check programme. NICE has also produced a guideline on population and community-level interventions for preventing type 2 diabetes. In September 2017, we reviewed the evidence for intensive lifestyle-change programmes and metformin for people at risk of type 2 diabetes. We added new recommendations on lifestyle-change programmes (recommendations 1.5.5 and 1.5.6) and changed the recommendation about offering metformin (recommendation 1.19.1).