A lighthouse is a shore-based structure designed to assist sailors with navigation. A classic lighthouse takes the form of a tall tower with a lamp assembly at the very top. The lamp creates a focused beam of light, which is rotated across the water in a pattern unique to that lighthouse. Navigational charts include a list of lighthouse patterns, allowing mariners to use lighthouses to orient themselves. In addition to serving as a navigational marker, a lighthouse also warns of hazards or it may point the way to the harbor mouth.

The earliest known lighthouse was the Lighthouse of Alexandria, on the island of Pharos. It was built in the third century BCE to assist sailors. Lighthouses were also used in the Middle East, with several historical accounts suggesting that the Muslim world in particular had an extensive system of lighthouses. In Europe, many lighthouses and watch towers were built, especially by the Romans, and when the Americas were settled, lighthouses soon followed.

Traditional lighthouses included living quarters for the lighthouse keepers. Early lighthouses which ran on oil lamps and hand wound clockwork required constant attention. Even as the systems became more automated, lighthouse keepers were needed to keep the mechanics of the lighthouse in order. Only in the later part of the twentieth century did lighthouses become automated enough that keepers were no longer needed. Modern automated lighthouses are highly efficient, although not nearly as majestic as classic lighthouses are.

In most cases, all of the lighthouses in a country are within the control of a government agency. The government keeps the lighthouses in good working order, although it may turn over ownership to private companies in some cases. In the United States, many private associations have taken over lighthouses to maintain the historical integrity of the structures. It is not uncommon to find a lighthouse with a bed and breakfast in the former keeper's quarters, or a lighthouse which offers educational programs for children.

Better navigational charts and equipment on board ships have reduced the necessity for lighthouses. However, before modern equipment became standard, a lighthouse could be a beacon of hope, indicating a harbor, or a warning of peril, suggesting dangerous shores or offshore shoals. The emblem of a lighthouse is often used symbolically to suggest guidance and hope by a variety of organizations. Christian organizations in particular favor the symbolism of the lighthouse, leading followers to Christian faith.