Haiphong or Hai Phong (Vietnamese: Hải Phòng, pronounced [hǎːj fɔ̀ŋ] ^ⓘ) is the third-largest city in Vietnam and is the principal port city of the Red River Delta. The municipality has an area of 1,526.52 km² (589.39 sq mi). The city includes Bạch Long Vĩ and Cát Hải islands in the Gulf of Tonkin. It has a population of 2,130,898 in 2023. The city's economy has strength in manufacturing, as evidenced by large industrial parks and numerous smaller traditional handicraft villages. Historically, Haiphong was the first place in Vietnam and Mainland Southeast Asia to get electricity.

In the imperial era of Đại Việt, the Bạch Đằng River in Haiphong was a place of many legendary victories, led by now-legendary commanders Ngô Quyền and Trần Hưng Đạo. In the 16th century, Mạc dynasty promoted the coastal settlement as a secondary capital, growing to become an important port town of Đàng Ngoài. After the French conquest of Vietnam, in 1888, the president of the French Third Republic, Sadi Carnot, promulgated a decree to establish Haiphong as one of the principal cities of French Indochina. From 1954 to 1975, Haiphong served as the most important maritime city of North Vietnam. It was one of the directly controlled municipalities of a reunified Vietnam with Hanoi and Ho Chi Minh City in 1976.

Haiphong is a popular seaside vacation spot and known for biological reserves in Cát Bà Island. For its extensive port, the city hosts the headquarters of the Vietnam People's Navy. Royal poinciana are commonly associated with Haiphong in Vietnamese culture.

Modern-day Haiphong was the home of Lê Chân, one of the female generals under the command of the Trưng Sisters who rose against Chinese domination in 40 AD and ruled until their defeat in 43 AD. Lê Chân was known to have established the Hải tần Phòng thủ (“Defenced Sea-coast”) during the war against general Ma Yuan of the Han dynasty. Centuries later under the reign of Nguyễn Emperor Tự Đức, the area earned the appellation: Hải-Dương thương-chính quan-phòng ("The trading defensive area of Hải Dương Province").

By the 19th century, at the end of Tự Đức's reign, the Hang Kenh Communal House in what is now the city's Le Chan District was made the administrative seat of An Dương District, restoring its regional importance. The area by then had developed into a sizable commercial port.

At the eve of the French conquest in 1881, a typhoon ravaged the area, killing about 3,000 people in and around Haiphong. Despite the damages, Haiphong was developed by the French to serve as Indochina's main naval base over the ensuing decades.

Following the defeat of Japan in World War II, Vietnamese nationalists agitated for independence against French return. French forces landed in Haiphong and encountered resistance which resulted in the deaths of three French soldiers. In retaliation, the French ships, among them the cruiser Suffren, shelled the city, setting it ablaze and precipitating the First Indochina War. French infantry forces under the command of Jean-Étienne Valluy entered the city, fighting house to house with the support of armored units and airplanes.

Late in the Vietnam War, Haiphong was subjected to heavy bombing by US Navy and Air Force strike aircraft because it was North Vietnam's only major port. U.S. Admiral Thomas H. Moorer ordered the mining of Haiphong harbor on 8 May 1972, effectively sealing the port. Until it was lifted, the mining caused no casualty. Despite being targeted, the physical structure of the city was mostly unaffected by the war as the US had a self-imposed prohibition zone for the city. After the war, the city recovered its role as a significant industrial center.