Acute-on-chronic liver failure (ACLF) has been defined differently in the East and West. The definitions given by Asian Pacific association for the study of liver (APASL) and American association for the study of liver (AASLD) and European association for the study of liver (EASL) working group have fundamental deficiencies and contradictions and do not encompass all patients with ACLF seen in the East and West. Although the World Gastroenterology Organisation (WGO) working party attempted to provide an improved definition but this too is not appropriate. In this article, we have compared the various definitions of ACLF given by APASL, EASL-AASLD and WGO and suggest a comprehensive definition for prospective collection of data on ACLF.