We can now isolate and manipulate antibody genes. Mouse antibodies can be humanized, resulting in chimaeric or reshaped antibodies. Antibody engineering is useful in large scale production of antibodies, in production of active antibody fragments, bifunctional, single-domain and catalytic antibodies, and has lead to the production of novel expression systems useful in many other areas. It allows production of new antibody conjugates, e.g. antibody-toxin or antibody-enzyme linked proteins. Engineered antibodies have many potential applications e.g. imaging, therapy and biosensors.