Hepatorenal syndrome (HRS) is a severe form of kidney impairment seen in patients with liver cirrhosis, marked by reduced renal blood flow and glomerular filtration rate. It occurs when kidney function declines, but there are no signs of intrinsic kidney disease, such as blood in the urine, protein in the urine, or abnormal kidney imaging. Unlike other types of acute kidney injury (AKI), HRS arises from functional changes in renal circulation and can potentially be reversed through liver transplantation or the use of vasoconstrictor medications. There are two main types of hepatorenal syndrome based on how quickly the kidney damage progresses. HRS-AKI refers to the acute form with rapid kidney function decline, while HRS-CKD (chronic kidney disease) describes a more gradual, long-term deterioration of kidney function. This chapter explores the key aspects of HRS, including its definition, underlying mechanisms, diagnosis, and treatment options.