This article reviews the role of proton therapy in the treatment of primary liver cancer focusing on hepatocellular carcinoma (HCC). The dose-sparing physical properties of protons are of great advantage in the treatment of HCC. To date, the clinical experience with the use of protons for HCC is encouraging. Most studies come from East Asia and show improved local control and survival with low toxicity. More importantly, when high-enough radiation doses are delivered to early liver cancers, a substantial fraction of patients are alive at 5 years, results not dissimilar from surgical resection. The technical details related to the use of proton therapy for HCC are also reviewed. The combination of proton therapy with other locoregional or systemic therapies is currently being tested and holds promise to improve survival while maintaining an acceptable level of toxicity.