The question of how metals are produced in the Universe and where they are located is fundamental for our understanding of galaxy formation and evolution. This question can be best addressed using absorption lines seen in the spectra of remote quasars. It has been realized that the spatial distribution of metals around galaxies and more generally in the Intergalactic Medium is complex, and it is often very difficult to associate one absorption system with one galaxy. Except for possibly in the special case of DLA systems, it may be more appropriate to discuss the clustering properties of different classes of objects and to measure their correlation functions. I illustrate these issues with three examples: the distribution of metals around galaxies at intermediate redshift, the modelling of the clustering of C IV systems, and the determination of abundances in Damped Lyman-α systems (and in particular the oxygen abundance). Finally, I note that there is a mass-metallicity relation in Damped Lyman-α systems.