Chronic kidney disease (CKD) poses a significant epidemiological challenge, necessitating effective patient management strategies. Nutritional intervention, particularly vitamin D supplementation, has garnered attention for its potential therapeutic utility in CKD. Despite widespread acknowledgment of the importance of vitamin D, particularly in bone and mineral metabolism, its supplementation in CKD patients for non-skeletal purposes remains contentious due to limited evidence. Hypovitaminosis D linked with CKD substantially contributes to disturbances in mineral and bone metabolism, increasing the risks of cardiovascular complications and skeletal disorders. Notably, CKD patients experience progressive vitamin D deficiency, exacerbating as the disease progresses. Guidelines recommend monitoring 25-hydroxyvitamin D (25 (OH)-D) levels due to their correlation with mineral metabolism parameters, although robust evidence for recommending supplementation is lacking. The primary aim of this paper is to focus on the main open questions regarding vitamin D supplementation in CKD, reporting the current evidence concerning the role of vitamin D supplementation in CKD and in renal transplant recipients.