As formal definitions of acute-on-chronic liver failure (ACLF) have now been established, and given an increased recognition of the dynamic nature of this condition, there is a growing clinical need to assess prognosis and response to interventions. Conventional scoring systems such as Model for End-Stage Liver Disease (MELD) fail to capture the two key prognostic elements in ACLF—namely, extrahepatic organ failure and measures of systemic inflammation—and as such are limited in their prognostic accuracy. Even the best available scoring systems such as the recently described CLIF (Chronic Liver Failure) Consortium ACLF (CLIF-C ACLF) score, are at best 75% accurate and need to be applicable to all etiologies of liver disease. Thus, in the absence of “gold standard” markers of prognosis that render one scoring system superior to another, there is a need to explore other markers of pathophysiology that may better define outcome. This review addresses the evidence for markers of oxidative stress, including those reflecting the inflammasome; elements of cell death such as cytokeratins M30 and M65; and indicators of immune dysfunction, innate immune failure and gut dysbiosis. Finally, evidence for relevance of markers of organ dysfunction, including hemodynamic response, are explored along with associated mediators such as copeptin, dimethylarginines, and renin. It is anticipated that further critique and validation of emerging and relevant biomarkers will facilitate a composite score which, either alone or in combination with existing scoring systems such as CLIF-C, will enable improved prognostication and targeting of therapy in ACLF.