Bt cotton is now being grown worldwide and adopted by many smallholders to overcome their bollworm problems. The management of the whole cotton cropping system is a key factor to ensure the sustainability of pest control by Bt cotton. Practices used in large-scale farming conditions to prevent insect resistance are no longer valid and there is controversy about the strategics to he adopted by smallholders. Modelling is a useful tool for simulating resistance patterns and developing strategies for sustainable bollworm management because many factors have to be considered when investigating the evolution of insect resistance in Bt crops. On the basis of preliminary laboratory results and field observations, we used a model to assess the significance of several of these factors in the Bt resistance process: The model highlighted some key factors: the initial level of resistance in wild populations, the heritability of resistance and the outmigration of resistant individuals from cotton fields at the end of the growing season. Some of these points could now be addressed on the basis of our current state of knowledge, but further research is needed to be able to gain insight into others.