Air defense refers to the measures taken to protect a country or region from attack by hostile aircraft or other airborne weapons. These measures can include a variety of systems and strategies, such as radar detection, anti-aircraft guns, surface-to-air missiles, and fighter aircraft. The purpose of air defense is to detect and intercept incoming threats before they can cause damage or harm.

In recent years, the topic of air defense has been in the news due to the conflict between Russia and Ukraine. The catchphrase "What Air Defense Doing?" was popularized by the North Atlantic Fellas Organization (NAFO) on Twitter and in video memes, used to mock the Russian military and Vladimir Putin while explosions were occurring in Crimea and elsewhere during August 2022, most likely from the Ukrainian air defense amid the Russian Invasion.

The United States has also been involved in efforts to bolster Ukraines air defense capabilities, forming a coalition focused on developing Ukraines air force in a bid to bolster that countrys long-term capability.