Insect cells have been successfully cultured in vitro as continuous cell lines for over 35 years. The media, culture methodology and conditions have been well resolved such that, for many insects, new cells lines can be routinely developed. Factors that are considered important for developing insect cell cultures are described as well as some of the history that led to the success. One of the major rationales for developing insect cell lines was for the study of insect viruses. This was particularly true for species of Lepidoptera from which over 900 viruses have been reported. Since many species of Lepidoptera are serious agricultural and forestry pests, effects have been made to utilize some of these pathogens as biological pesticides. Cell cultures are important in this endeavor since viruses require a living cell to reproduce. Of the known insect viruses, the most intensely studied have been the baculoviruses. In addition to their potential for controlling insect pests, they also have been used as expression vectors for producing recombinant proteins. Details of some of these experiments are described. Finally, experiences with insect cells are considered in relation to efforts to develop prawn cell cultures.