Gene-cloning processes enable us to produce large amounts of a DNA sequence so that its function can be studied. These technologies can also be applied in medicine and agriculture to genetically engineer production of biological proteins or whole organisms with new or modified traits. At the heart of these applications is the capability to produce recombinant proteins from cloned genes in host cells. ‘Genetic engineering’ outlines some of these applications: recombinant pharmaceuticals, monoclonal therapeutic antibodies, recombinant protein vaccines, gene therapy, and genetically modified foods. It also considers some of the concerns with these applications.