Advanced Cell Technology (ACT), a stem cell biotechnology company in Worcester, Massachusetts, showed the potential for cloning to contribute to conservation efforts. In 2000 ACT researchers in the United States cloned a gaur (Bos gaurus), an Asian ox with a then declining wild population. The researchers used cryopreserved gaur skin cells combined with an embryo of a domestic cow (Bos taurus). A domestic cow also served as the surrogate for the developing gaur clone. The successful procedure opened the opportunity to clone individuals from species for which there are few or zero live specimens. The official release of this experiment's data was published in the paper 'Cloning of an Endangered Species (Bos gaurus) Using Interspecies Nuclear Transfer,' in October 2000. In the article, the researchers presented data collected from several cloned fetuses that were aborted before the full term of 283 days. At the time of publication, the gaur bull fetus, named Noah at birth, had developed for greater than 180 days. Noah was born on 8 January 2001, but died two days later due to dysentery. The development, birth, and death of Noah became a platform for conservationists and ethicists to critique the role of cloning in society and as a method to conserve species.

In 1995 and 1996, researchers at the Roslin Institute in Edinburgh, Scotland, cloned mammals for the first time. Keith Campbell, Jim McWhir, William Ritchie, and Ian Wilmut cloned two sheep, Megan and Morag, using sheep embryo cells. The experiments indicated how to reprogram nuclei from differentiated cells to produce live offspring, and that a single population of differentiated cells could produce multiple offspring. They reported their results in the article 'Sheep Cloned by Nuclear Transfer from a Cultured Cell Line' in March 1996. This experiment led the Roslin team to later clone mammals from adult body cells and to genetically engineer mammals.

The Roslin Institute was established in 1993 in the village of Roslin, Scotland, as an independent research center by the Biotechnology and Biological Sciences Research Council (BBSRC), and as of 2014 is part of the University of Edinburgh in Edinburgh, Scotland. Researchers at the Roslin Institute cloned the Dolly the sheep in 1996. According to the Roslin Institute, Dolly was the first mammal to develop into an adult from the transfer of the nucleus of an adult sheep cell into an ovum with the nucleus removed. The Roslin Institute performs genetic and medical based animal studies to help investigate human physiology and medicine and to improve agricultural research. The Roslin Institute studies embryology, cloning, hormones, and genetic alterations in animals and techniques such as Somatic Cell Nuclear Transfer (SCNT).

Keith Henry Stockman Campbell studied embryo growth and cell differentiation during the twentieth and twenty-first centuries in the UK. In 1995, Campbell and his scientific team used cells grown and differentiated in a laboratory to clone sheep for the first time. They named these two sheep Megan and Morag. Campbell and his team also cloned a sheep from adult cells in 1996, which they named Dolly. Dolly was the first mammal cloned from specialized adult (somatic) cells with the technique of somatic cell nuclear transfer (SCNT). Campbell helped develop cloning techniques that used a common form of connective tissue cells (fibroblasts). Besides working at the Roslin Institute, in Edinburgh, Scotland, for most of his career, Campbell also taught at the University of Nottingham in Nottingham, England.

In 2006, Kazutoshi Takahashi and Shinya Yamanaka reprogrammed mice fibroblast cells, which can produce only other fibroblast cells, to become pluripotent stem cells, which have the capacity to produce many different types of cells. Takahashi and Yamanaka also experimented with human cell cultures in 2007. Each worked at Kyoto University in Kyoto, Japan. They called the pluripotent stem cells that they produced induced pluripotent stem cells (iPSCs) because they had induced the adult cells, called differentiated cells, to become pluripotent stem cells through genetic manipulation. Yamanaka received the Nobel Prize in Physiology or Medicine in 2012, along with John Gurdon, as their work showed scientists how to reprogram mature cells to become pluripotent. Takahashi and Yamanaka's 2006 and 2007 experiments showed that scientists can prompt adult body cells to dedifferentiate, or lose specialized characteristics, and behave similarly to embryonic stem cells (ESCs).

In the 1990s, researchers working at the Roslin Institute in Edinburgh, Scotland, performed cloning experiments in collaboration with PPL Therapeutics in Roslin, Scotland, on human coagulation factor IX, a protein. The team of scientists used the methods identified during the Dolly experiments to produce transgenic livestock capable of producing milk containing human blood clotting factor IX, which helps to treat a type of hemophilia. By using a cell's resting state, called quiescence, or G0, and transferring modified nuclear material from one cell to an egg cell that had had its nuclear material removed, the researchers developed a method to produce genetically modified mammals, including humans. Angelika E. Schnieke, Alexander J. Kind, William A. Ritchie, Karen Mycock, Angela R. Scott, Marjorie Ritchie, Ian Wilmut, Alan Colman, and Keith H. S. Campbell published the results of their experiments as Human Factor IX Transgenic Sheep Produced by Transfer of Nuclei from Transfected Fetal Fibroblasts (hereafter called Human Factor IX). The article details the methods that produced the cloned sheep named Polly, as well as other cloned and genetically altered sheep.

Dizhou Tong, also called Ti Chou Tung, studied marine animals and helped introduce and organize experimental embryology in China during the twentieth century. He introduced cellular nuclear transfer technology to the Chinese biological community, developed methods to clone organisms from many marine species, and investigated the role of cytoplasm in early development. Tong's administrative and scientific leadership in the fields of marine, cellular, and developmental biology contributed to China's experimental embryology research programs.

In the 1990s, Ian Wilmut, Jim McWhir, and Keith Campbell performed experiments while working at the Roslin Institute in Roslin, Scotland. Wilmut, McWhir, and Campbell collaborated with Angelica Schnieke and Alex J. Kind at PPL Therapeutics in Roslin, a company researching cloning and genetic manipulation for livestock. Their experiments resulted in several sheep being born in July 1996, one of which was a sheep named Dolly born 5 July 1996. Dolly was the first sheep cloned and developed from the nuclei of fully differentiated adult cells, rather than from the nuclei of early embryonic cells. They published their results in Viable Offspring Derived from Fetal and Adult Mammalian Cells (abbreviated Viable Offspring) on 27 February 1997.

To educate its citizens about research into chimeras made from human and non-human animal cells, the United Kingdom's Human Fertilisation Embryology Authority published the consultation piece Hybrids and Chimeras: A Consultation on the Ethical and Social Implications of Creating Human/Animal Embryos in Research, in 2007. The document provided scientific and legal background, described ethical and social issues associated with research using part-human part-animal embryos, supplied a questionnaire for citizens to return to the HFEA with their opinions, and offered a list of resources for further reading to stimulate public debate. The strategy of surveying the public provided a template for developing further policy in the United Kingdom and other countries, as well as for educating citizens on embryological research.

In 2007, the Human Fertilisation and Embryology Authority in London, UK, published Hybrids and Chimeras: A Report on the Findings of the Consultation, which summarized a public debate about research on, and suggested policy for, human animal chimeras. The HFEA formulated the report after conducting a series of surveys and debates from earlier in 2007. The HFEA issued a statement in September 2007, followed by an official report published on 1 October 2007. Their report on human-animal chimeras set a worldwide precedent for discussions of the ethical use of those embryos in labs. The HFEA's report led the UK government to pass legislature about the use of human-animal cytoplasmic hybrid embryos for research in the UK.