The genus Aspergillus, a representative group of filamentous fungi, is intricately linked to human life and the natural environment. Species within this genus play essential ecological roles, undergoing complex cycles of growth and asexual and sexual development. Most Aspergillus species produce asexual spores known as conidia, which can contaminate or infect plants, animals, and humans, causing opportunistic or pathogenic infections. Aspergillus species are prolific producers of secondary metabolites. While some of these compounds, such as mycotoxins, pose significant health risks to humans and animals, others—such as the cholesterol-lowering drug lovastatin—have important pharmaceutical applications. A network of internal genetic factors and external environmental cues tightly regulate both fungal development and secondary metabolism. In this chapter, we review recent advances in our understanding of the molecular mechanisms governing asexual and sexual development, as well as the biosynthesis of secondary metabolites, in Aspergillus species.