A target is a protein, enzyme, receptor, ion channels, signaling, or other molecule that may play a role in a particular disease. The discovery and therapeutic strategy is typically focused on the target molecule or process. In Appendix B, the nature of currently known targets that play roles in diseases and examples of the corresponding approved drugs are presented. Based on the level of target de nition presented, Imming et al. (2006) has estimated 218 targets for approved drugs. In a more recent paper, Landry and Gies (2008) have found that there are about 330 targets for approved drugs; 270 of them are encoded by the human genome and 60 belong to pathogenic organisms. In contrast, an analysis of the human genome carried out in 2002 led to the estimation that there are 6000-8000 targets of pharmacological interest (cited in Landry and Gies, 2008).