Mass production of insects is a core activity to address the global demand for animal proteins for food and feed, one of the top societal and environmental priorities in Europe and worldwide. Mass-reared insects are also crucial for pollination, fishery, biocontrol of pest insects, animal and human disease prevention, and organic waste debris conversion. Insect farming generally occurs under high density monoculture conditions in specialised insect rearing facilities. In such “insect factories” insect pathogens easily emerge, leading to extensive economic losses for the companies involved. The number of European insect producers has considerably increased over recent years, as has the scale at which they produce insects. However, the success of these companies is heavily relying on healthy insects. To be sustainable and cost-effective insect production urgently needs to become more resilient to a large range of pathogens. However, at the start of the INSECT DOCTORS programme, knowledge on the pathogens that threaten mass-reared was very scarce. Furthermore, a shortage of sufficiently qualified people, highly knowledgeable in the breadth of disciplines within insect pathology (e.g. bacteriology, virology, mycology), was apparent. The INSECT DOCTORS double-degree network was initiated to overcome the gaps in knowledge described above and to train a new generation of insect pathologists with relevant skills and expertise to benefit the insect mass rearing industry. The research performed in INSECT DOCTORS aimed to increase our understanding of insect pathogens and how and under which circumstances they impact mass-reared insects. Furthermore, we aimed to develop improved rearing methods to reduce the risk of disease outbreaks in a variety of produced insects (e.g. crickets, mealworms, wax moths, fruit flies), as well as the tools to diagnose insect pathogens in commercial insect rearing settings.