Restenosis remains a major limitation of percutaneous coronary interventions. Numerous studies including pharmacological approaches and new devices failed to reduce the restenosis rate except coronary stenting. Since the results of BENESTENT1) and STRESS2) studies came out, coronary stenting has been the most popular interventional strategy in the various kinds of coronary stenotic lesions, although the efficacy of stenting was shown only in the discrete lesion of the large coronary artery. The widespread use of coronary stenting has improved the early and late outcomes after coronary intervention, but it has also led to a new and serious problem, e.g., in-stent restenosis. Intravascular radiation for prevention of restenosis is a new technology in the field of percutaneous coronary intervention. Recent animal experiments and human trials have demonstrated that local irradiation, in conjunction with coronary interventions, substantially diminished the rate of restenosis. This paper reviews basic radiation biology of intracoronary radiation and its role in the inhibition of restenosis. The current status of intracoronary radiation therapy using Re-188 liquid balloon is also discussed.