For patients who are not able to receive oral or enteral nutrition, parenteral nutrition (PN) is a life-saving therapy. Since the late 1960s, PN has been used in both adults and pediatric patients. In 1971, hepatobiliary complications were described in infants on total parenteral nutrition (TPN) by Peden et al. for the first time (Peden et al. J Pediatr 78(1):180–181, 1971). Since then, a variety of adverse effects caused by TPN have been recognized. Liver cirrhosis caused by prolonged total parenteral nutrition is a rare but potentially life-threatening complication. It marks the end stage of parenteral nutrition-associated liver disease (PNALD). Usually, intestinal failure (IF) indicates the use of TPN. Liver injury can occur not only as a consequence of PN but also secondary to intestinal failure (intestinal failure–associated liver disease (IFALD)). A clear differentiation between IFALD and PNALD is difficult and, in clinical practice, sometimes impossible. Both terms are often used interchangeably in the literature, which results in a wide range of prevalence and incidence. Pathogenesis of PNALD is multifactorial, and it is challenging to distinguish between the role of the underlying condition (e.g., extensive small bowel resection) and that of PN in pathogenesis (Plauth et al. Clin Nutr 38(2):485–521, 2019). In this chapter, we conform to the nomenclature of the European Society for Clinical Nutrition and Metabolism (ESPEN). The term PNALD is used to emphasize the role of parenteral nutrition in the pathogenesis of liver injury, but “liver injury can occur not only as a sequel of PN (termed PNALD) but also by intestinal failure (termed IFALD)” (Plauth et al. Clin Nutr 38(2):485–521, 2019; Bischoff et al. Clin Nutr 39(12):3533–3562, 2020). The term IFALD “refers to a liver injury as a result of one or more factors relating to IF, including, but not limited to, PN” (Lal et al. Clin Nutr 37(6):1794–1797, 2018; Pironi et al. Clin Nutr 35(2):247–307, 2016).