For flying animals, including many birds, bats, and insects, the air is a crucial arena for a range of behaviors. Technological advances, such as year-round tracking of flight altitudes and expanded use of radar, increasingly show how flying animals use the aerial habitat. This enables us to answer questions about the environmental patterns and ecological processes that shape aerial niches, including energetics, biotic interactions, and risk due to growing anthropogenic conflicts. In this review, we identify environmental conditions and biological interactions influencing where animals occur in the airspace throughout their life cycles. We outline an ecological framework to advance understanding of how different properties of the airspace shape fundamental aerial habitat niches and how biotic interactions influence the realized niches.