Antibodies are outstanding tools for biomedical research and essential components of a myriad of diagnostic tests. They are also the largest and fastest growing source of new drugs. The vast majority of therapeutic antibodies are made using recombinant DNA technology, which has enabled the engineering of specific functions and the reduction or elimination of undesirable side-effects. However, protein engineering has largely been ignored during the development of antibodies for diagnostics and research, where most are still made by immunising goats or rabbits (“polyclonal” antibodies) or using hybridoma cells (“monoclonal” antibodies).