In the last two weeks, several new university rankings were published. Since universities are facing ever tougher competition, their placement in university rankings becomes increasingly important. So, I’ll spend a couple of blogs on rankings, how the lists are constructed, and what one needs to take into consideration in their interpretation. It struck me that the business of ranking has become more sophisticated over the years. Now that rankings are an instrument for universities in the competition for resources, researchers and students, the competition between them is also increasing. This can work to increase the quality of these rankings, on the other hand it might also promote an overly simple interpretation. Ranking is a complicated business, because it means that a complex phenomenon such as quality, which is by definition composed of many independent dimensions, is reduced to a one-dimensional list. The attraction of rankings is exactly this reduction of reality to an ordered list in which one’s position is unambiguous. This also means that ranking is an inherently problematic business. For example, a university may have high quality teaching as its core mission. This means this university may not score high in a ranking that does not really take teaching into account. In other words, if one wants to evaluate the performance of an institution, one should take into account its mission. It would still be a difficult task to squeeze the complex network of performances of institutions into a simple ordered list. And perhaps we should abstain from ordered lists as such, and develop a completely new form of presentation of performance data. The importance of university missions and the fact that quality is a complex phenomenon that has many different aspects, is central in a European research project lead by CHEPS in which CWTS also participates. This project may produce a new way of monitoring university performance. But for now, we are stuck with one-dimensional rankings. There are five different university rankings that are commonly used, and I will spend a blog on each of them in the course of this week. These are: the Times Higher Education Supplement ranking, the QS ranking (a spin-off of the THES ranking), the Leiden ranking produced by CWTS, the Shanghai ranking, and the somewhat lesser-known Web of World Universities ranking. In the next blog, I’ll discuss how rankings are being used by universities, then I will discuss each ranking in more detail, to conclude with some ideas about the future of rankings.