Monoclonal antibodies or antibody fragments (Fabs and single chain) are gaining attention in diagnostic and therapeutic applications. Such molecules are generally expressed in mammalian cells or transgenic systems in order to enable proper folding and glycosylation. A variety of expression systems are being explored, microbial systems (E. coli, Filamentous fungi and Yeast), transgenic plants as well as transgenic animals. Antibody fragments are produced in high density E. coli processes, and aglycosylated antibodies have also been expressed in E. coli. Among other microbial systems, Yeast Saccharomyces cerevisiae system has been developed based on twin-cassette expression technology for full-length monoclonal antibodies, and Methylotrophic yeast Pichia pastoris system has also been developed with modified strains developed to produce human like glycosylation. Transgenic plants are also being used for the production of plantibodies by several groups. The presentation will cover overview of various expression systems currently being developed by different groups.