In this chapter we will present methods for determination of the quality of mass reared egg parasitoids. Before we describe quality controlquality control guidelines, we will first outline the development of quality control of natural enemies, summarize the basic considerations concerning management of laboratory populations, and discuss obstacles in mass rearingmass rearing that may lead to deterioration of natural enemy quality. We consider a discussion of the above topics essential for understanding practical quality control guidelines, because without a proper theoretical background, relevant guidelines cannot be developed. Where possible, we have illustrated background theory with examples from the egg parasitoid literature.