Abstract: Most of the world’s ant species rely on flight for reproduction and dispersal, during a solitary phase in which colony fitness depends only on the survival of individual queens. Flight-related selection shapes ant physiology, such that queens and males fly for short durations but carry heavy loads due to the nutrient demands of mating and colony founding. Ants vary by four orders of magnitude in flight distance, with larger ants or those with lighter abdomens flying farther than smaller or heavier ones. Flight tradeoffs explain much variation in ant life history, including the temporal segregation of flight and egg production, the continuum of ant mating systems from male aggregation to female calling syndromes, and the evolution of alternate colony founding strategies. Flight performance also constrains range expansions or shifts in response to invasions or climate change. Flying queens and males act as dispersal vectors for pathogenic or symbiotic organisms, and are eaten in large numbers by aerial insectivores. By entering aerial food webs, flying ants help mediate the flow of energy and materials through ecosystems. They are also model systems for addressing several questions, including nutrient allocation tradeoffs and the evolution of reproductive polymorphisms.