Silkworms (Bombyx mori) have emerged as highly efficient, cost-effective living bioreactors for large-scale recombinant protein production, offering superior cell-density capacity and accurate post-translational modifications compared to conventional bacterial and yeast expression systems. This chapter provides a comprehensive overview of silkworm-based gene expression technologies. It details the principles of the baculovirus expression system (BES), emphasizing the strategic use of strong viral promoters (e.g., polh, p10) and effective gene insertion techniques. To overcome the time-consuming purification processes of traditional BES, the BmNPV bacmid system is highlighted as a rapid, scalable, and biosafety-enhanced platform for transient protein expression in both larvae and pupae. Furthermore, the chapter explores the generation of transgenic silkworms utilizing the piggyBac transposon system. This approach enables stable, multigenerational integration of large foreign genes without genetic footprints. By targeting gene expression to specific silk-gland regions, recombinant proteins can be seamlessly incorporated into the silk cocoon’s fibroin core or sericin layer, enabling simplified extraction. Together, these advanced expression systems position silkworm biotechnology as a highly promising and economically viable solution to meet the growing global demand for complex biopharmaceuticals and recombinant proteins.