Ōta is a special ward situated within the Tokyo Metropolis in Japan. Located as the southernmost of the twenty-three special wards, it shares borders with Shinagawa, Meguro, and Setagaya to the north, and Kōtō to the east. The Tama River forms its southern and western boundaries, separating it from Kawasaki in Kanagawa Prefecture. Administratively, it functions as a distinct municipal entity within the greater Tokyo urban area.

The ward was established on March 15, 1947, through the merger of the former Ōmori and Kamata wards following Tokyo City's transformation into the Tokyo Metropolis. Its name derives from combining characters from both predecessor names. It previously held the second-largest area status until land reclamation for Haneda Airport expansion allowed it to surpass Setagaya as the largest special ward by area.

Notable districts include Kamata, which serves as the administrative center, and Den-en-chōfu, an exclusive residential area known for luxury homes. The ward contains Haneda Airport, Japan's busiest airport by passenger traffic. Other landmarks feature Ikegami Honmon-ji, Heiwajima Park, and Senzokuike Park. The area also holds historical significance as the site of former Allied prisoner of war camps during World War II.

Cultural institutions include the Ota City Local History Museum and the Katsu Kaishū Memorial Museum. Visitors can explore the Omori Nori Museum and the Shōwa Era Lifestyle Museum, which is housed in a renovated 1951 residence. The ward offers access to Haneda Airport observation decks and various grave sites of notable historical figures, providing insight into local heritage and artistic traditions.

As of 2024, the estimated population is 744,849, making it the third largest special ward by population with a density of 12,041 inhabitants per square kilometre. The economy features headquarters for companies like Canon and ANA Wings. Transportation is extensive via JR East, Keikyu, and the Tokyo Monorail. The ward maintains international ties with sister cities including Salem in Massachusetts.