A harbor or harbour (see spelling differences), or haven, is a body of water where ships, boats and barges seek shelter from stormy weather, or are stored for future use. Harbors and ports are often confused with each other. A port is a manmade facility built for loading and unloading vessels and dropping off and picking up passengers. Ports are often located in harbors.

Harbors can be natural or artificial. An artificial harbour can have deliberately constructed breakwaters, sea walls, or jettys, or they can be constructed by dredging, which requires maintenance by further periodic dredging. An example of an artificial harbour 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 twentieth century.

In contrast, a natural harbour is surrounded on several sides by prominences of land. Examples of natural harbours include Sydney Harbour, Australia and Trincomalee Harbour in Sri Lanka.

Artificial harbors

Artificial harbours are frequently built for use as ports. The oldest artificial harbour 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 BC, reign of King Khufu). The largest artificially created harbour is Jebel Ali in Dubai. Other large and busy artificial harbours include:

The Ancient Carthaginians constructed fortified, artificial harbours called cothons.

Natural harbors

A natural harbour in Vizhinjam, India

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

Ice-free harbors

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

The world's southmost harbor, located at Antarctica's Winter Quarters Bay (77° 50′ South), is potentially ice-free, depending on the summertime pack ice conditions.

Important harbors

The tiny harbour at the village of Clovelly, Devon, England
Old Harbor in Lüneburg, Germany.
The harbour of Piraeus in Greece.
The harbour of Gorey, Jersey falls dry at low tide.
Punta del Este's harbour – nicknamed the Monte Carlo of South America
The harbour in Aberystwyth, painted c. 1850

Although the world's busiest port is a hotly contested title, in 2006 the world's busiest harbour by cargo tonnage was the Port of Shanghai.

The following are large natural harbors:

Other notable harbours include: