On Relational Properties of Lumpability A. Sokolova and E.P. de Vink The technique of lumping of Markov chains is one of the main tools for recovering from state explosion in the quantitative analysis of large probabilistic systems. Useful results regarding relational properties of general, ordinary and exact lumpability, in particular transitivity and strict confluence, are rather scattered or implicit in the literature. These are collected and reformulated here from a process-theoretic point of view. Additionally, counterexamples are provided that complete the picture.