Traditional models of sexual selection often emphasize how males compete for and females choose between mates. However, mate choice does not end with finding a suitable mate. In this presentation, I will take a deeper look into the complex processes of post-mating sexual selection, using Drosophila fruit flies as a model system. Here, innovative techniques and large-scale experimental work has allowed us to gain critical insights into the evolution of reproductive traits and the complex interplay between genetic, physiological, and behavioral factors that shape competitive fertilization and ultimately reproductive success.