Abstract: Could there be a meaningful framework for reasoning about clustering independently of any particular algorithm, objective function or generative data model? A formal mathematical axiomatization of clustering tasks could shed light on the merits and limitations of different clustering approaches, provide model selection principles, as well as help discover novel clustering paradigms. However, the task seems elusive and there has been surprisingly little work pursuing the development of such a framework. I shall discuss several attempts to provide an abstract axiomatic basis for the definition, taxonomy and analysis of clustering. I shall outline the current state of knowledge and present some concrete significant open questions along this line of research.