A bookmobile or mobile library is a vehicle designed for use as a library. They have been known by many names throughout history, including traveling library, library wagon, book wagon, book truck, library-on-wheels, and book auto service. Bookmobiles expand the reach of traditional libraries by transporting books to potential readers, providing library services to people in otherwise underserved locations (such as remote areas) and/or circumstances (such as residents of retirement homes). Bookmobile services and materials (such as Internet access, large print books, and audiobooks), may be customized for the locations and populations served.
Bookmobiles have been based on various means of conveyance, including bicycles, carts, motor vehicles, trains, watercraft, and wagons, as well as camels, donkeys, elephants, horses, and mules.
In the United States of America, The American School Library (1839) was a traveling frontier library published by Harper & Brothers. The Smithsonian Institution's National Museum of American History has the only complete original set of this series complete with its wooden carrying case.
The British Workman reported in 1857 about a perambulating library operating in a circle of eight villages, in Cumbria. A Victorian merchant and philanthropist, George Moore, had created the project to "diffuse good literature among the rural population".
The Warrington Perambulating Library, set up in 1858, was another early British mobile library. This horse-drawn van was operated by the Warrington Mechanics' Institute, which aimed to increase the lending of its books to enthusiastic local patrons.
During the late 1800s, Women's Clubs began advocating for Bookmobiles in the state of Texas and throughout the United States. Kate Rotan of the Women’s Club in Waco, Texas was the first to advocate for bookmobiles. She was president of the Texas Federation of Women's Clubs (TFWC). During this time Women's Clubs were encouraged to promote bookmobiles because they embraced their ideas and missions. After receiving so much support and promotion these traveling libraries increased in numbers all around the United States. In the state of New York from 1895 to 1898 the number of bookmobiles increased to 980. The United States Women Clubs became their primary advocate. 
The Women’s Club movement in 1904, had the standard to be held accountable for the influx of bookmobiles in thirty out of fifty states. Because of the Texas Federation of Women’s Clubs (TFWC), a new legislation to develop public libraries in Texas became possible after much advocating from TFWC for bookmobiles. This new legislation brought in library improvements and expansions that included, establishing a system of traveling libraries in Texas. Women’s Clubs wanted state governments to step in and create commissions for these traveling libraries. They hoped the commissions would boost the managers of the bookmobile’s “Library Sprit”. Unfortunately, the Texas Library Association (TLA) could not provide the type of service that is already provided to state libraries to bookmobiles. 
One of the earliest mobile libraries in the United States was a mule-drawn wagon carrying wooden boxes of books. It was created in 1904 by the People's Free Library of Chester County, South Carolina, and served the rural areas there.
Another early mobile library service was developed by Mary Lemist Titcomb (1857–1932). As a librarian in Washington County, Maryland, Titcomb was concerned that the library was not reaching all the people it could. The annual report for 1902 listed 23 "branches", each being a collection of 50 books in a case that was placed in a store or post office throughout the county. Realizing that even this did not reach the most rural residents, the Washington County Free Library began a "book wagon" in 1905, taking the library materials directly to people's homes in remote parts of the county.
With the rise of motorized transport in America, a pioneering librarian in 1920 named Sarah Byrd Askew began driving her specially outfitted Model T to provide library books to rural areas in New Jersey. The automobile remained rare, however, and in Minneapolis, the Hennepin County Public Library operated a horse-drawn book wagon starting in 1922.
Following the Great Depression in the United States, a WPA effort from 1935 to 1943 called the Pack Horse Library Project covered the remote coves and mountainsides of Kentucky and nearby Appalachia, bringing books and similar supplies on foot and on hoof to those who could not make the trip to a library on their own. Sometimes these "packhorse librarians" relied on a centralized contact to help them distribute the materials.
At Fairfax County, Virginia, county-wide bookmobile service was begun in 1940, in a truck loaned by the Works Progress Administration ("WPA"). The WPA support of the bookmobile ended in 1942, but the service continued.
The "Library in Action" was a late-1960s bookmobile program in the Bronx, NY, run by interracial staff that brought books to teenagers of color in under-served neighborhoods.
Bookmobiles reached the height of their popularity in the mid-twentieth century.
In England, bookmobiles, or “traveling libraries” as they were called in that country, were typically used in rural and outlying areas. However, during World War II, one traveling library found popularity in the city of London. Because of air raids and blackouts, patrons did not visit the Metropolitan Borough of Saint Pancras's physical libraries as much as before the war. To meet the needs of its citizens, the borough borrowed a traveling library van from Hastings and in 1941 created a “war-time library on wheels.” (The Saint Pancras borough was abolished in 1965 and became part of the London Borough of Camden.)
The Saint Pancras traveling library consisted of a van mounted on a six-wheel chassis powered by a Ford engine. The traveling library could carry more than 2,000 books on open-access shelves that ran the length of the van. The books were arranged in Dewey order, and up to 20 patrons could fit into the van at one time to browse and check out materials. A staff enclosure was at the rear of the van, and the van was lighted with windows in the roof – each fitted with black-out curtains in case of a German bombing raid. The van could even be used at night, as it was fitted with electric roof lamps that could access electrical current from a nearby lamp-standard or civil defense post. The traveling library had a selection of fiction and non-fiction works; it even had a children’s section with fairy tales and non-fiction books for kids.
The mayor of the borough christened the van with a speech, saying that “People without books are like houses without windows.” Even after heavy night bombings by the Germans, readers visited the Saint Pancras Traveling Library in some of the worst bombed areas.
Bookmobiles are still in use in the 21st century, operated by libraries, schools, activists, and other organizations. Although some[who?] feel that the bookmobile is an outmoded service, citing reasons like high costs, advanced technology, impracticality, and ineffectiveness, others cite the ability of the bookmobile to be more cost-efficient than building more branch libraries would be and its high use among its patrons as support for its continuation. To meet the growing demand for "greener" bookmobiles that deliver outreach services to their patrons, some bookmobile manufacturers have introduced significant advances to reduce their carbon footprint, such as solar/battery solutions in lieu of traditional generators, and all-electric and hybrid-electric chassis. Bookmobiles have also taken on an updated form in the form of m libraries, also known as mobile libraries in which patrons are delivered content electronically.
The Internet Archive runs its own bookmobile to print out-of-copyright books on demand. The project has spun off similar efforts elsewhere in the developing world.
The Free Black Women's Library is a mobile library in Brooklyn. Founded by Ola Ronke Akinmowo in 2015, this bookmobile features books written by black women. Titles are available in exchange for other titles written by black female authors.
In the U.S., the American Library Association sponsors National Bookmobile Day in April each year, on the Wednesday of National Library Week. They celebrate our nations bookmobiles and the dedicated library professionals who provide this service to their communities.
In February 2021, the American Library Association (ALA), the Association of Bookmobile and Outreach Services (ABOS), and the Association for Rural and Small Libraries (ARSL) agreed to rebrand National Bookmobile Day in recognition of all that outreach library professional do within their communities. Instead, libraries across the country will observe National Library Outreach Day on April 7, 2021. Formerly known as National Bookmobile Day, communities will celebrate the invaluable role library professionals and libraries continuous play in bringing library services to those in need. 
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Suomen ensimmäinen liikkuva kirjasto toimi nykyisen Vantaan kaupungin, entisen Helsingin maalaiskunnan, alueella 1913–14.