Animals have been in use in the drug research and development process in lieu of providing safety and efficacy data in the past several decades, especially after the thalidomide and sulphanilamide tragedies. But due to various reasons like continuous pressure from animal welfare groups all over the world and continuous advancements in the field of non-animal alternative testing strategies, demand for substitution of animals to ascertain drug safety is catching momentum. The 3R'principle i.e. reduction, refinement and replacement approach has become the motto of humane treatment towards experimental animals around the world. In this process validation of different alternative methods is the need of the hour and hence different national and international organizations like Organization for Economic Cooperation and Development, International Cooperation on the Validation of Alternative Methods, etc. are making and implementing guidelines for it. Keeping in view the changing scenario in regard to restriction on testing of animals across the globe, this book updates reasons and development of alternatives to the use of animals in drug research and approval process.