Insulin glargine 100 units/ml (Gla-100) has become a standard of care in diabetes treatment over the past decade, providing 24-h basal insulin coverage after once-daily subcutaneous injection for many people with diabetes, with a well-established efficacy and safety profile. New insulin glargine 300 units/ml (Gla-300) is a basal insulin that provides the same number of units as Gla-100 in a third of the volume. Compared with Gla-100, Gla-300 has shown more constant and prolonged pharmacokinetic (PK)/pharmacodynamic (PD) profiles. This review summarizes the findings from the EDITION series of clinical trials that investigated Gla-300 in individuals with type 1 and type 2 diabetes mellitus. Overall, Gla-300 has been shown to achieve similar glycaemic control with less, or similar, nocturnal hypoglycaemia compared with Gla-100, and a trend towards lower hypoglycaemia at any time of day. The EDITION series of clinical trials also provides some evidence for less weight gain with Gla-300 than with Gla-100. In addition, the PK/PD profiles of Gla-300 may allow more flexibility in the timing of doses, improving convenience; thus, Gla-300 could offer several positive features for individuals with diabetes requiring basal insulin therapy.