Bacillus thuringiensis (Bt) has been the leading biopesticide against lepidopterous pests since 1959. In the 1990 s the following developments contributed to increased rational uses of Bt: (1) natural and recombinant Bt products were developed to broaden the insect host range in pest management programs; (2) new formulations based on conventional or genetically engineered encapsulation of the toxins and/or feeding stimulants to increase ingestion and, in turn, the efficacy of the microbe; (3) screening of the interactions of Bt with insect herbivores and plant allelochemicals or natural enemies of the pests, to aid the formulation of biological control strategies; and (4) knowledge and management of insect resistance to Bt. The prospects for Bt insecticides will be described and discussed. 