Diabetic macular oedema (DMO) is the most frequent cause of vision loss in patients affected by diabetes mellitus, and has a remarkable effect on public health. The treatment with focal/grid laser photocoagulation was considered in the past decades as the standard of care, but the recent advent of new pharmacological approaches, based on the use of intravitreal anti-vascular endothelial growth factor (anti-VEGF), has completely revolutionised the management of DMO. The most important molecule of this class of drugs is represented by ranibizumab, which has been clinically supported by several randomised clinical trials. The present review aims at providing a comprehensive summary of the most important investigations regarding the ranibizumab treatment of DMO.