Insulin is a biologic product used in the treatment of all patients with type 1 diabetes and in a substantial proportion of patients with type 2 diabetes. When a licensed insulin product reaches the end of its patent life, the market opens for biosimilar products. These are copies of the originator insulin intended to be clinically equivalent to the licensed product. Numerous technical challenges are encountered in producing and manufacturing a biosimilar insulin, one of which is that by nature of the manufacturing process of a biological product, it cannot be an identical copy of the original. Given the time and expense that is required to develop a biosimilar insulin, it is imperative that the clinical development programs for these compounds are carefully managed at all stages.