Graph coloring has been a field of attraction for many years; a wide collection of papers has been dedicated to the study of chromatic properties of graphs. Initially such problems were just a kind of game for pure mathematicians; it was in particular the case of the famous four color problem. However, as people were getting used to applying the tools of graph theory for solving real-life organizational problems, chromatic models appeared as a quite natural way of tackling many situations. Among these are timetabling problems, or more generally scheduling with disjunctive constraints (pairwise incompatibility between jobs), clustering in statistics, automatic classification, group technology in production (partitioning a collection of parts into families of parts which are as similar as possible in their production process), VLSI design, etc.