Global university rankings uncovered: introduction

University rankings have gained growing attention from university administrations and faculty members, markets, governments, mass media and the public at large, affecting nearly all aspects directly or indirectly related to academia. This Theme Section includes 12 essays from 16 authors, coming from 9 countries (i.e. Singapore, the USA, the UK, Ireland, Belgium, Germany, Spain, Cyprus and Greece). These essays cover different methodological, socio-political, econom- ical and ethical 'hot issues' emerging from the dominance of rankings in the higher education sec- tor through the views and thoughts of different stakeholders (i.e. university administrators, people involved in performing the rankings, and scientists). We hope that this Theme Section and the questions it raises will further contribute to the recent debate and future of university rankings, whether they be global or regional, as well as help find the nexus between numbers (i.e. rankings) and knowledge (i.e. higher education institutions); to paraphrase Plato's quote 'a good decision is based on knowledge and not on numbers'.