Nowadays rankings are everywhere. Nonetheless, the methodology of rankings receives little attention. This is worrisome, because how a ranking was developed influences ranking results. The development of rankings may be supported by the Delphi method: a structured group communication process in which data are collected from experts in several subsequent rounds with the aim of allowing these experts to achieve agreement on a particular topic. As the potential of the Delphi method for developing rankings had hardly been explored, this PhD thesis set-out to find an answer on the following general research question: What are
the methodological challenges and opportunities of the Delphi method for
developing rankings? Six studies were conducted that together show how the Delphi method may be used to: (1) obtain a ranking of objects (e.g. cities) on a ranking attribute (e.g. urban sustainability), and (2) help define and measure complex ranking attributes (e.g. urban sustainability).