During the 1990s a series of projects carried out at Monash University, together with reference to studies in Europe, USA and Brazil, have led to the development of recommendations for performance criteria for rear underride (or underride) barriers for heavy vehicles over 3.5 tonne. The work focussed on the development and crash testing of high capacity, yet practical, rigid and energy absorbing systems catering for both centred as well as offset impacts. The limitations of current international regulations are discussed, and recommendations for improved performance criteria to achieve effective rear underride barriers are presented.