Global university rankings have cemented the notion of a world university market arranged in a single "league table" for comparative purposes and have given a powerful impetus to intranational and international competitive pressures in the sector. Both the research rankings by Shanghai Jiao Tong University and the composite rankings by the Times Higher Education Supplement have been widely publicised and already appear to have generated incentives in favour of greater system stratification and the concentration of elite researchers. However, global comparisons are possible only in relation to one model of institution, that of the comprehensive research intensive university, and for the most part are tailored to science-strong and English-speaking universities. Neither the Shanghai nor the Times rankings provide guidance on the quality of teaching. It is important to secure "clean" rankings, transparent, free of self-interest, and methodologically coherent, that create incentives to broad-based improvement. © 2007 Nuffic.