This chapter introduces instances of insect cell fusion studies. Fusion between the cells of the same cell line species was first attempted by J. L. Becker with Echalier and Ohanessian's Drosophila melanogaster cell line. An attempt of electrofusion between insect cells and plant protoplasts has been made. One of the reasons establishment of a technique of insect cell fusion has seemingly been abandoned may be lack of prospective application of insect hybrid cells. Hybrid cells may find their use to enhance production of insect pathogenic microorganisms for microbial control. There are methods to use mutant cell clone or strain, which lack some normal cell function, as parent cells to facilitate isolation of hybrid cells. Since demonstration of cell fusion by a virus, hemagglutinating virus of Japan (HVJ), the HVJ has been used widely to fuse vertebrate cells.