MicroRNAs are a class of small regulatory RNAs that function to modulate protein expression. This control allows for fine‐tuning of the cellular phenotype, including regulation of proliferation, cell signaling, and apoptosis; not surprisingly, microRNAs contribute to liver cancer biology. Recent investigations in human liver cancers and tumor‐derived cell lines have demonstrated decreased or increased expression of particular microRNAs in hepatobiliary cancer cells. Based on predicted and validated protein targets as well as functional consequences of altered expression, microRNAs with decreased expression in liver tumor cells may normally aid in limiting neoplastic transformation. Conversely, selected microRNAs that are up‐regulated in liver tumor cells can promote malignant features, contributing to carcinogenesis. In addition, microRNAs themselves are subject to regulated expression, including regulation by tumor suppressor and oncogene pathways. This review will focus on the expression and function of cancer‐related microRNAs, including their intimate involvement in tumor suppressor and oncogene signaling networks relevant to hepatobiliary neoplasia. (HEPATOLOGY 2009.)