Diabetes is justly recognized as an emerging global epidemic, representing one of the leading causes of morbidity and mortality worldwide. Hyperglycemia, the common characteristic of both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM), has the potential to cause serious complications due to its insidious and chronic nature. The present special issue has been designed to publish original and review articles highlighting recent fundamental advances in our understanding of diabetic complications. Emphasis has been given on the underlying molecular mechanisms, the new technologies that have been introduced to facilitate early diagnosis, and the new potential therapies for these complications. There are 30 articles in total, which cover 6 thematic areas: pathogenesis of diabetic complications, diabetic neuropathy, nephropathy, retinopathy, macrovascular complications, and miscellaneous complications.