A museum ship, or sometimes memorial ship, is an old ship that has been preserved and converted into a museum open to the public. There are several hundred of these around the world, often associated with maritime museums.

Despite the long history of sea travel, the ravages of the elements and the expense of maintenance has resulted in the destruction of nearly all the ships that were ever built, usually by being broken up and sold for scrap. Only a few have survived, sometimes because of historical significance, but more often simply due to luck and circumstance.

Since an old ship tied up at dockside, without attention, will still decay and eventually sink, the practice of recent years has been to form some sort of preservation society, solicit donations from governments and the wealthy, organize volunteer labor from the enthusiasts, and open the restored ship to visitors, usually for a fee.

The restorations have presented an interesting set of problems for historians, who are frequently asked for advice, and the results periodically generate some controversy. For instance, the rigging of sailing ships has almost never survived, and so the rigging plan must be reconstructed from various sources.

Typically the visitor enters via gangplank, wanders around on the deck, then goes below, usually precariously down the original stairways, giving a sense of how the crew got around. The interior features restored but inactivated equipment, enhanced with mementos including old photographs, interesting pages from the ship's logs, menus, and the like. Some will add recorded sound effects to heighten the sense of "being there."

A number of the larger museum ships have begun to offer hosting for weddings, meetings, and other events, sleepovers, and on a few ships still seaworthy, cruises. In this category is the Constitution's annual "turnaround," where the old ship is towed out into the harbor and brought back in facing the other way, so as to weather evenly. A place on the deck is by invitation only, and highly prized.

The tourism appeal of a city waterfront graced by an interesting old vessel is such that most port cities of the world now have at least one museum ship, even if it has meant building a replica at great expense.

The first museum ship is reported to be Jason's Argo, which after his expedition for the Golden Fleece, was preserved on a beach and shown to visitors for ages afterwards.

Notable Museum Ships

Main article: List of museum ships

• HMS Belfast - London, cruiser
• USS Constitution - Boston, oldest commissioned warship afloat
• Cutty Sark - Greenwich, only surviving clipper ship
• Mayflower - Plymouth, Pilgrims ship (replica)
• USS Midway - San Diego, largest aircraft carrier museum.
• USS Missouri - Pearl Harbor, battleship
• USS Nautilus - Groton, Connecticut, first nuclear-powered submarine
• Star of India - San Diego, oldest active ship
• Wasa - Stockholm
• HMS Victory - Portsmouth, oldest intact warship
• Bluenose II - Lunenburg, Nova Scotia
• USCGC Taney - Last ship still afloat that participated in the attack on Pearl Harbor
• USS Intrepid - New York City, aircraft carrier
• Rap - Horten, Norway, first torpedo boat
• USS Lexington (CV-16) - Corpus Christi, Texas, United States, World War II aircraft carrier