Although heavy elements ("metals") are formed in galaxies, they are known to exist in substantial quantities in the intergalactic medium by their signature in quasar absorption spectra. I will start by reviewing the question of how they got there, and what we can learn about cosmology from them. Then, I will review recent observational analyses detailing the amount, distribution, evolution, and temperature of the enriched IGM. Finally, I will discuss the comparison of observed quasar absorption spectra to cosmological simulations including chemical enrichment.