Genetic engineering, recombinant DNA technology, genetic modification/manipulation (GM) and gene splicing are terms applied to the direct manipulation of an organism's genes. Genetic engineering is not to be confused with traditional breeding where the organism's genes are manipulated indirectly. Genetic engineering uses the techniques of molecular cloning and transformation. Genetic engineering endeavors have found some success in improving crop technology, the manufacture of synthetic human insulin through the use of modified bacteria, the manufacture of erythropoietin in Chinese hamster ovary cells, and the production of new types of experimental mice such as the oncomouse (cancer mouse) for research.

Since a protein sequence is specified by a segment of DNA called a gene, novel versions of that protein can be produced by changing the DNA sequence of the gene. Some groups have argued that genetic engineering is wrong and is "doing the work of God", but most scientists believe that genetic engineering is essential to help future medical discoveries.

However, even with regard to this technology's great potential, some people have raised concerns about the introduction of genetically engineered plants and animals into the environment and the potential dangers of human consumption of GM foods. They say that these organisms have the potential to spread their modified genes into native populations thereby disrupting natural ecosystems. See also GM food controversies, and genetically modified organism (GMO) for more information on GM controversies.