A harbor ( American English), or harbour ( Australian English, British English, Canadian English, Irish English, New Zealander English; see spelling differences), is a sheltered body of water where ships, boats, and barges can be moored. The term harbor is often used interchangeably with port, which is a man-made facility built for loading and unloading vessels and dropping off and picking up passengers. Harbors usually include one or more ports. Alexandria Port in Egypt, meanwhile, is an example of a port with two harbors.

Harbors may be natural or artificial. An artificial harbor can have deliberately constructed breakwaters, sea walls, or jetties or they can be constructed by dredging, which requires maintenance by further periodic dredging. An example of an artificial harbor is Long Beach Harbor, California, United States, which was an array of salt marshes and tidal flats too shallow for modern merchant ships before it was first dredged in the early 20th century. ^[1] In contrast, a natural harbor is surrounded on several sides by land. Examples of natural harbors include Sydney Harbour, New South Wales, Australia, Halifax Harbour in Halifax, Nova Scotia, Canada and Trincomalee Harbour in Sri Lanka.

Artificial harbors are frequently built for use as ports. The oldest artificial harbor known is the Ancient Egyptian site at Wadi al-Jarf, on the Red Sea coast, which is at least 4500 years old (ca. 2600-2550 BCE, reign of King Khufu). The largest artificially created harbor is Jebel Ali in Dubai. ^[2] Other large and busy artificial harbors include:

• Port of Houston, Texas, United States
• Port of Long Beach, California, United States
• Port of Los Angeles in San Pedro, California, United States
• Port of Rotterdam, Netherlands
• Port of Savannah, Georgia, United States

The Ancient Carthaginians constructed fortified, artificial harbors called cothons.

A natural harbor is a landform where a section of a body of water is protected and deep enough to allow anchorage. Many such harbors are rias. Natural harbors have long been of great strategic naval and economic importance, and many great cities of the world are located on them. Having a protected harbor reduces or eliminates the need for breakwaters as it will result in calmer waves inside the harbor. Some examples are:

For harbors near the North and South poles, being ice-free is an important advantage, especially when it is year-round. Examples of these are:

• Hammerfest, Norway
• Liinakhamari, Russia
• Murmansk, Russia
• Nakhodka in Nakhodka Bay, Russia
• Pechenga, Russia
• Prince Rupert, Canada
• Valdez, United States
• Vardø, Norway
• Vostochny Port, Russia

The world's southernmost harbor, located at Antarctica's Winter Quarters Bay (77° 50′ South), is sometimes ice-free, depending on the summertime pack ice conditions. ^[3]

Although the world's busiest port is a contested title, in 2017 the world's busiest harbor by cargo tonnage was the Port of Ningbo-Zhoushan. ^[7]

The following are large natural harbors:

• Media related to Harbours at Wikimedia Commons
• The dictionary definition of harbor at Wiktionary
• Harbor Maintenance Finance and Funding Congressional Research Service
• "Harbor" . New International Encyclopedia. 1905.