Toxicogenomics was first described in 1999 as the application of omic technologies (genomics, transcriptomics, proteomics and metabolomics) to the study of toxicology. Today the definition should be expanded to include epigenomics. The omic disciplines represented a continuum of biological information starting with the genome, which is then regulated by the epigenome to give rise to the transcriptome, which in turn encodes the proteome and finally the actions of the proteome give rise to the metabolome (Figure 1). Since its inception toxicogenomics has primarily focus on the identification of biomarkers that diagnose or predict disease. In addition it has been used extensively to shed light on the molecular mechanisms and key events that lead to toxicity.