Diabetic nephropathy (DN) is a concept based on histopathological diagnosis, confirmed when diabetes-specific glomerular lesions—such as nodular glomerulosclerosis or diffuse mesangial expansion—are observed. In contrast, diabetic kidney disease (DKD) is a clinical diagnosis applied as a comprehensive concept when (1) kidney damage is observed in the presence of diabetes and (2) diabetic pathophysiology is presumed to be involved in its progression. The classical course of DN is characterized by a progression from glomerular hyperfiltration to microalbuminuria, then overt proteinuria, and eventually a decline in eGFR. In contrast, DKD includes the following three non-classical subtypes in addition to this typical pattern.