Metals in the intergalactic medium

The absorption lines seen in the spectra of quasars trace gas over a very l arge range of overdensities, from galaxies to voids and probably account fo r most of the baryons at high redshift. Once thought to be a chemically pri stine remnant of the Big Bang, the Lyman alpha forest has now been shown to contain significant quantities of metals. We summarise the results of the latest searches for weak C IV lines in low density regions of the intergala ctic medium together with recent theoretical work aimed at understanding th e origin of such widespread metal pollution and what it can tell us about t he first generations of stars.