AIMS: Insulin efsitora alfa (efsitora) is a once-weekly basal insulin. This review describes the study design and rationale of the efsitora phase 3 Once Weekly (QW) Insulin Therapy (QWINT) clinical development programme, including the five trials, QWINT-1 through QWINT-5. MATERIALS AND METHODS: The five trials included insulin-naïve adults (QWINT-1 and -2) with type 2 diabetes (T2D), adults with T2D previously treated with basal insulin (QWINT-3 and -4), and QWINT-5 in adults with type 1 diabetes. All five trials were designed as multicentre, randomized, controlled, open-label, treat-to-target studies to investigate the efficacy and safety of efsitora versus active once-daily basal insulin comparators (insulin glargine U100 or insulin degludec U100). The primary objective of each trial is to compare the change in HbA1c from baseline to week 26 or 52 between efsitora and the active comparator. The key secondary objectives include change in fasting glucose, insulin dose and continuous glucose monitoring variables, and patient-reported outcome questionnaires. CONCLUSIONS: The QWINT development programme includes a racially and geographically diverse population to provide important information regarding the efficacy and safety of efsitora and its clinical management of people with diabetes.