As well as being a metabolic factory, the liver also functions as a powerful immune organ constantly engaged in local immune responses. In addition, it has a significant influence on systemic immunity. The hepatic immune system recognises and responds to pathogens, as well transformed and metastatic cells, while at same time tolerising harmless dietary and commensal antigens. The molecular mechanisms by which these different discriminatory, regulatory and effector functions are mediated are only now beginning to be identified.