Insulin Degludec (IDeg) is a basal insulin with a unique mode of protraction and a duration of action greater than 42 hours. The Phase 3a development program induced seven trials in patterns with Type 1 and Type 2 diabetes, which demonstrated HbA1c non-inferiority of IDeg to insulin glargine U100 (IGlar) with lower rates of nocturnal confirmed hypoglycaemia. Potential limitations of the phase 3a data included the lack of blinding, inclusion of non-symptomatic hypoglycaemia, exclusion of patients with at least one risk factor for hypoglycaemia, and no recording of the timing of IGlar administration. SWITCH 1 and 2 was designed to confirm the hypoglycaemia benefit previously seen, address these limitations, and assess the safe switch to IDeg from other insulins. In these two double-blind crossover trials in pateitns with type 1 and type 2 diabetes, IDeg achieved superiority for both the primary and confirmatory secondary hypoglycaemia endpoints compared with IGlar U100. In SWITCH 2 for type 2 diabetes patients, the rate of severe or BG confirmed symptomtic hypoglycaemia, severe or BG-confirmed symptomatic nocturnal hypoglycaemia and severe hypoglycaemia were lower by 30%, 42% during the maintenance period and 51% during the full treatment period. In SWITCH 1 for type 1 diabetes patients, the rate of severe or BG confirmed symptomtic hypoglycaemia, severe or BG-confirmed symptomatic nocturnal hypoglycaemia and severe hypoglycaemia were lower by 11%, 36% and 35% respectively during the maintenance period. There was no apparent difference between IDeg and IGlar for the standard efficacy parameters or in terms of adverse events.