Cloning refers to asexual organisms through somatic cell breeding, and the populations are composed of individual offspring with exact the same genotype formed by asexual organisms, usually, it means the process that asexual organism produces its offspring that owns exactly the same genotype with original individual by utilizing biological technology. The cloning has a very broad application prospect, but it is also controversial on whether human should use it or how to use it. This book is one of the series of Scientific Frontiers in the 21st Century.