The kidneys are vital organs that play an essential role in maintaining the internal homeostasis of the human body. They remove metabolic waste products and toxins, regulate fluid and electrolyte balance, contribute to blood pressure control, and participate in several endocrine functions. Importantly, kidney function is closely connected with the health of other organs, including the brain. The concept of the kidney–brain axis has therefore gained increasing attention because impaired kidney function is associated with neurological and cognitive abnormalities. When kidney function declines, particularly in chronic kidney disease (CKD), various metabolic waste products accumulate in the circulation. These substances, known as uremic toxins, include compounds such as indoxyl sulfate and p-cresyl sulfate, as well as several gut-derived metabolites. Some of these retained solutes may affect the vascular system and nervous tissue and may contribute to disruption of the blood–brain barrier, which normally protects the brain from potentially harmful circulating substances. Chronic kidney disease is also associated with increased oxidative stress, systemic inflammation, endothelial dysfunction, and neuroinflammation. These processes can impair neuronal function and communication between brain cells. Consequently, patients with CKD may experience difficulties involving attention, memory, processing speed, and executive functions. Cognitive impairment becomes particularly important in advanced kidney disease and among patients receiving dialysis. Several additional factors may contribute to the kidney–brain relationship. Hypertension, anemia, abnormalities in calcium and phosphate metabolism, vascular disease, and impaired cerebral blood flow can increase the vulnerability of the brain. Therefore, cognitive dysfunction in CKD is considered multifactorial and cannot be attributed to uremic toxins alone. Instead, vascular, metabolic, inflammatory, oxidative, and toxic mechanisms may interact and contribute to neurological dysfunction. Interestingly, some studies have reported improvement in certain aspects of cognitive performance following kidney transplantation, suggesting that at least part of the neurological dysfunction associated with advanced kidney failure may be partially reversible after restoration of renal function. In conclusion, maintaining healthy kidney function is important not only for urinary and metabolic health but also for protecting brain function. Early detection and appropriate management of CKD, together with effective control of hypertension, diabetes, and cardiovascular risk factors, may help reduce the neurological and cognitive consequences associated with impaired renal function. Understanding the kidney–brain axis may also contribute to the development of future strategies aimed at protecting cognitive health in patients with kidney disease. Al-Mustaqbal University the First in Iraq