Summary: Iron deficiency is a common cause of anemia in patients with chronic kidney disease (CKD), and iron supplements, together with erythropoiesis-stimulating agents (ESAs), remain the cornerstones of the therapy. CKD patients may have either absolute or functional iron deficiency. Absolute iron deficiency is defined by severely reduced or absent iron stores. It is diagnosed when the transferrin saturation (TSAT) is below or equal to 20%, and the serum ferritin concentration is below or equal to 100 ng/ml among predialysis and peritoneal dialysis patients or below or equal to 200 ng/ml among hemodialysis patients. In contrast, in functional iron deficiency, the iron stores are adequate; however, they cannot be utilized for erythropoiesis due to the iron blockade in the reticuloendothelial system, which is characterized by TSAT below 20%, and elevated ferritin levels. This article shortly reviews the pathophysiology of iron deficiency in CKD, the indications for iron therapy, currently available oral and intravenous iron-repletion agents, and the choice of iron therapy in non-dialysis and dialysis patients.