The process of asexual reproduction observed, for example, in bacteria and other unicellular micro-organisms which divide by simple fission, so that the daughter cells are genetically identical to each other and to the parent (except when mutation occurs). In higher organisms, genetically identical individuals may be produced by cloning. A body (somatic) cell is taken from an embryo in an early stage of development or from an adult, the nucleus transferred to an unfertilized ovum from which the nucleus has been removed, and the product grown in culture; daughter cells from the earliest divisions are removed, and grown in culture or implanted into host mothers to give genetically identical offspring. The successful cloning of a sheep (named Dolly, 1996–2003) was reported by scientists from the Roslin Institute, Edinburgh, UK, in February 1997. There is considerable potential application in animal rearing, but its application to humans is extremely unlikely (except in some rare instances of in vitro fertilization). The term molecular cloning is used in recombinant DNA technology, where a section of foreign DNA is inserted into an artificial bacterial chromosome (plasmid) and divides with it, thus ‘cloning’ the DNA.

In 1998, a Council of Europe protocol banning the cloning of human beings was signed in Paris by 19 states - the first international treaty on the issue. However, in 1999, predictions were being made about the application of the technique in other areas, such as bone-marrow grafting in leukaemia, and transplant medicine in general, and the controversy surrounding the ethics of human cloning continued to exercise professional and public opinion. In 2004, Newcastle University received Britain's first licence to clone human embryos. In early 2006, Dr Hwang Woo-suk, a South Korean scientist working at Seoul National University, was disgraced when he admitted that his recently published research on human stem cells had been fabricated.