Antibody based drugs have not only advanced the prevention and treatment of a number of life threatening diseases including cancer and arthritis, but have also provided the thrust for the continued success of the biopharmaceutical and pharmaceutical industry. Currently at least seven therapeutic antibodies are listed among the top ten revenue generating pharmaceutical products. These antibodies are generally monoclonal in origin and include, chimerised, humanised and human antibody types. Recently, new classes of antibody drugs are emerging and are expected to be among the next generation of block buster drugs within the Industry. These new classes include antibody conjugates, bispecific antibodies and antibody fragments. In this chapter, we will discuss the methods used for the production of antibodies in both hybridoma and non-hybridoma cells lines. The chapter will also focus on the successful use of these antibodies as therapeutics in cancer and rheumatoid arthritis.