TARGIT is an international randomised clinical trial designed to test the hypothesis that the strategy of delivering a single dose of targeted intraoperative radiotherapy (IORT) in patients eligible for breast conserving therapy (with the addition of whole breast radiotherapy in those patients at high risk of recurrence elsewhere in the breast [e.g. lobular carcinomas and extensive intraductal component]) is equivalent to a conventional course of post-operative external beam radiotherapy (EBRT). The primary endpoints are local and loco-regional recurrence rates. It is a pragmatic trial in which each participating centre has the option to define more restrictive entry criteria than in the core protocol. Only centres with access to the Intrabeam® (Carl Zeiss) enter patients into the trial. Eligible patients are those with tumours of good prognosis suitable for breast conserving surgery. After giving consent patients are randomised to either IORT or to EBRT. They may receive any other adjuvant treatments as deemed necessary, except for neoadjuvant therapy. The protocol requires that patients be followed at six monthly intervals for five years and then annually.