In the quoted defense of animal-based research, a number of examples where experiments on animals have played a role in the development of vaccines and therapeutic treatments are listed. Most researchers, including the authors of this chapter, agree that research with animals has contributed to the development of life sciences and medicine over the last centuries. However, it is much more difficult to say with a reasonable degree of certainty what would have been achieved if animals had not been used. It seems likely that animals will continue to play a central role in biological and biomedical research in the foreseeable future, much as they do today. Current practice can be summarized by saying that experimental animals are used for three main purposes: to develop pharmaceutical and other medical products, to advance fundamental research in the life sciences, and to test the safety of potentially toxic products and substances. A rough idea of the relative numbers of animals used in these ways (in Western countries at least) is conveyed by recent data indicating that, of the experimental animals used in the European Union in 2005, more than 60% of animals were used in ContEnts