The beneficial macroorganisms that can be used for plant protection are extremely diverse and often very difficult to identify. This taxonomic diversity is accompanied by extremely varied adaptations that ultimately have a major impact on the effectiveness of biological control strategies. As a result, being able to initially identify these species and continue to do so reliably are major challenges. Inaccurate characterization of natural enemies during the research and development phase or during field applications leads indeed to suboptimal or even failed pest regulation. In this chapter, we begin with an overview of the taxonomic diversity of macroorganisms and illustrate the range of antagonistic interactions with their target pests. We then present integrative systematics, a discipline that combines various approaches (such as morphological study, which includes genitalia, DNA sequencing and especially barcoding, etc.). This discipline is now key to identifying and understanding interactions between species. Finally, we look at three cross-cutting themes from an eco-evolutionary perspective: ecological specialization, behavioural adaptations (host/prey location) and diversity of symbionts in natural enemies.