Insulin degludec is a new-generation basal insulin with an ultra-long duration of action. The insulin degludec and insulin degludec/insulin aspart clinical trial programme was truly global, involving 40 different countries and encompassing a multitude of ethnic populations. It is the largest insulin development clinical trial programme on record--with more than 11,000 patients included worldwide. It includes two main components: BEGIN (insulin degludec studied across the spectrum of diabetes) and BOOST (insulin degludec in a fixed-dose combination with insulin aspart). In clinical trials (phase 2 and phase 3a), insulin degludec achieved similar glycaemic control to that seen with insulin glargine in patients with type 1 or 2 diabetes, but with a lower risk of nocturnal hypoglycaemia. In addition, trials examining a flexible dosing regimen of insulin degludec in patients with type 1 or 2 diabetes show the potential for adjusting the injection time, without compromising glycaemic control or safety. A 200 U/mL formulation of insulin degludec is also available for use in patients who require large volumes of basal insulin. Subcutaneous insulin degludec is generally well tolerated in patients with type 1 or 2 diabetes and represents a useful advance in the treatment of type 1 or 2 diabetes.