Museums can be traced back over 2,000 years to private collections of wealthy individuals. Public museums started in the late middle ages. The Capitoline Museums were founded in 1471 and opened to the public in 1734. The Vatican Museums date back to 1506. The Royal Armouries in the Tower of London opened to the public in 1660. However, museums did not become widespread until the 19th and 20th centuries.

Museums are typically created to preserve historic artifacts, to educate and to enable research; though the term is not legally protected, and does not in itself warrant academic aspirations. Many museums are established by national and local governments or by universities, educational charities or non-profit organisations. A few museums are run as profit-making commercial ventures, while others are run as a spin-off from commercial or military organisations, to promote their products or public image. There are also museums created as a private hobby, perhaps later receiving public or community support. "Museums" on sensational topics such as erotica or torture might be disappointing tourist traps; check reviews before going. Curation policy within museums can also vary considerably.

A museum may be as simple as a small room with a narrowly focussed collection, perhaps opened one day per week by a volunteer. Other museums, typically national or regional museums, are in large buildings housing a wide variety of exhibitions. Open-air museums can include a village or town.

Extant and former monarchies usually have some of their palaces in use as museums. Former celebrity homes can also be converted to museums, including those of scientists, artists and politicians, such as the Presidents of the United States.

Older museums have become historical artifacts in their own right, for their architecture, for their collections, or for their scientific legacy. Buildings and collections which were contemporary when the museum was inaugurated, might centuries later seem obsolete, but also be rare examples of earlier exhibition methods and ideologies. Up to the 18th century, most collections were only intended to be seen by higher social classes. Since the 19th century, museums took on the assignments to create and romanticize national identity, and to contribute to public education.

Some museums specialize in items from their own region or country, but it is also fairly common to find some with exhibits whose origins are far away. Some of this goes back to imperialist history, when many of these items were controversially looted from their places of origin; the British Museum famously has items from Greece, Egypt, India, Africa, China and other places, and some of those countries have asked Britain to send them back. Similarly, French museums have much art from Africa and Indochina, American museums have art from Hawaii and the Philippines, Russian museums have art from Central and Eastern Europe, and so on.

The World Cultures Museum in Frankfurt has a fine collection of totem poles, made by natives on the northwest coast of Canada and the US, and the Royal Ontario Museum in Toronto has an excellent exhibit on Ancient China.

Guided tours are usually possible and may even be free. In certain museums a guided tour may be the only way visitors are allowed in. Some museums offer guided tours of the surroundings, in particular if it is an archaeological site, an old town, or a historically important site.

In addition to or instead of guided tours, there may be self-guided audio tours or maps showing you the layout of the museum. These typically show you the locations of all the exhibits, or rooms, in relation to the museum in general.

Self-guided audio tours and brochures are often available in a selection of languages. Guided tours in other than the local language(s) may be available at certain hours or days of the week, or by agreement. Sometimes it is possible to ask questions in languages other than the one of the tour. Unless you know the local language it usually pays to check the options.

Most museums are divided into exhibits, and the bigger the museums the larger the exhibits, the fancier the exhibits, and the more exhibits there are.

Museums, especially if oriented towards kids, may have performances or interactive activities. Science museums in particular often have elaborate interactive exhibits exploring scientific phenomena. Sometimes there are planetariums in which you can view documentary films about space; the movie screens in planetariums are so large that watching them can cause motion sickness.

Museums may have tours, often showing parts of the museums that are not accessible to the general public.

See also: Art and antiques shopping

There will often be a souvenir shop on-site. Most museums see this shop not as a public service but as a source of profit that can subsidise other portions of the museum's operation, which do serve the institution's core mission. The items therefore can be overpriced; often, they might not serve any purpose except as a souvenir. These souvenirs may however be unique items. Sometimes the items are made for use, with a twist reminding of the museum, such as a deck of cards in historic style.

It is also common for museums to sell replicas of items in their collections, or even items held by other museums. Museums at archaeological sites are particularly likely to offer replicas. Major museums like the British Museum or the Smithsonian have a wonderful selection, and even lesser museums often have some quite fine stuff. Many of these items are rather pricey, but quality is usually excellent and many items are unique. Where else could you get a good copy of some of Cleopatra's jewellery, or of an ancient statue as in the photo?

If a museum is engaged in research, they may have one or more books in print. These publications are specialised and usually closely related to the subject matter covered in the museum's main collections. An art gallery might sell photographs or postcards depicting individual works in its collections. Very occasionally, a museum or gallery will have an associated book-store.

The food at museum cafes or restaurants is likely to be overpriced; therefore, if the museum is in a city with other restaurants within walking distance, you may be able to save money by getting your meal at a restaurant outside the museum. Many museums won't let you back in after you leave (at least not without paying admission again), which means that if you anticipate spending more than an hour or two inside it's a good idea to eat first.

If the museum restaurant is nice, you may however regard the price as part of your contribution to the museum. At living history sites the restaurant may serve something meant to feel like period dishes, sometimes best-effort, sometimes obviously quasi-historic.

While most museums (and their curators) are not hôteliers or pub and tavern landlords, a few organise occasional sleepovers aimed at children (typically around 10 years old, maybe with a parent). The kids spend one night in a museum gallery with activities in the evening before bedding down in a sleeping bag.

Another exception is the open-air living museum which recreates an entire village. A restored tourist ghost town or pioneer village may slip one or two modern, working businesses into the otherwise-historic village, disguising them to look (from the outside) to be period-appropriate. Behind the genteel façade of the village inn that served the community a century or two ago in the museum's depicted time period is a modern hotel or a modern pub; step inside and the illusion of being in the colonial pioneer era may be quickly shattered by the electric hum of refrigerators and the glow of fluorescent light.

In a museum, especially one with valuable or historically significant objects on display, you must have respect toward the objects being shown. A general principle is that you should not touch anything on display unless a sign says "Please touch" or something similar.

While some museums and galleries allow photography of their collections, others don't. This is sometimes for commercial reasons, but is more commonly for security or conservation concerns (the flash needed for taking photographs in the otherwise purposely dim light can harm works of art or other precise crafts), or to maintain a specific atmosphere. If you want to take photos, in the absence of specific notices, it's generally best to ask first, especially if you plan on using a flash gun or tripod. You may also want to check copyrights on works of art displayed in a museum, especially if you are a professional photographer.

Museums can be found all over the world. Even small cities will often have one or two, maybe to educate visitors about local history or display some local resident's unusual interest. In many nations, there will be an extensive collection of museums in the national capital, showcasing the history, creative works (like paintings and films), or scientific developments of the capital city or the country as a whole.

Many universities, especially the more prestigious ones, also run museums of their own, covering a wide range of topics. Perhaps the most famous of such museums is the University of Oxford's Ashmolean Museum, but there are also numerous other world-class ones, including the University of Pennsyvania's Penn Museum, the University of Chicago's Oriental Institute and Stanford University's Cantor Arts Center.

Some cities are famous for high concentrations of excellent museums:

• Africa
  • Cairo
• Asia
  • Beijing
  • Tokyo

• Europe
  • Amsterdam
  • Berlin
  • Florence
  • London
  • Moscow
  • Madrid
  • Oxford
  • Paris
  • Rome (including the Vatican)
  • Saint Petersburg
  • Stockholm
• North America
  • Chicago
  • Los Angeles
  • Mexico City
  • New York City
  • Pittsburgh
  • Philadelphia
  • Washington, D.C.
• Oceania
  • Melbourne

Some of our articles such as paleontology and gemstones have lists of museums with good exhibits on their topics.

• Archaeological sites
• Living history museums
• UNESCO World Heritage List