The relatively new technique of positron emission tomography (PET) that incorporates both anatomy and function is increasingly being utilized in oncological imaging. This review assesses the use of PET of the liver for optimal and appropriate patient clinical management. The role of PET in both liver-lesion detection and characterization is discussed (including the context of primary liver malignancy, hepatocellular carcinoma, cholangiocarcinoma, metastatic disease from colorectal cancer and other tumor types). The use of functional PET imaging for prognostication, efficacy pre-liver transplantation, response assessment including post-radio frequency ablation and Yttrium-90 radioembolization, as well as the emerging and future roles of novel PET biomarkers, is also highlighted.