Aeroallergens are airborne particles that trigger and exacerbate allergic disease in susceptible individuals. They include pollen grains, fungal spores, dust mites, and animal dander. The production, distribution, and bioavailability of these allergens are shaped by the interplay of environmental, biological, and meteorological factors, as well as climate change. The concentration and potency of allergens is on the rise, contributing to greater disease burden. This chapter reviews the major sources of aeroallergens in North America, their dynamic behavior across diverse environments, and their impact on human health. Interdisciplinary collaboration and enhanced monitoring of both allergens and the environment are essential for developing targeted interventions to mitigate the adverse effects of allergens in a changing climate.