Laboratory animals have a long history of use since human started the practice of medicine. The early days of laboratory animal use saw a high growth phase. During this period, science progressed a lot with many vaccines and drugs. However, ethics and welfare were not given much importance. The awareness on animal ethics and a need to control laboratory animal research was felt in the middle of the twentieth century. Since then, there was some decline in the use of animals. Activism and public interest in the field of animal usage ensured restrictions in animal usage and welfare measures.

While the importance of welfare was stressed, it was realized that animals play a crucial role in the development of science and continuous research. Countries across the globe started bringing in regulations regarding use of animals. Governments stepped in to regulate animal usage. Now a balancing act is required by the stakeholders, viz. the veterinarians, the scientists, management, and the regulators. On one side, many interesting developments in animal research including use of newer species such as zebra fish, gene knockouts, and humanized animal models are revolutionizing in the field of in vivo research. On the other hand, emphasis on 3Rs (Replacement, Reduction and Refinement) and the implementation of severity classification and humane endpoints have made the field of in vivo studies thought-provoking and meaningful.