The techniques which allow dna fragments from different sources (different chromosomes, different organisms, or man-made) to be recombined to make new dna molecules with unique features. Humans have been manipulating dna for a long time using selective breeding. In the 70"s dna was hard to work with at the molecular level. Individual genes are contained amongst other genes in a long, linear polymer: the composition of most dna"s are similar as they are composed of only. 4 bases, therefore, traditional biochemical approaches were not well suited for separating and analyzing individual genes: now the manipulation of genes in the lab is easy using the tools of recombinant dna technology. Slow: limited by the breeding time of the organism and chance genetic events. Rapid: as quick as a few days in some organisms. No limitations you can put a human gene in bacteria. Has allowed the rapid expansion of scientific knowledge.