A bookmobile or mobile library is a vehicle designed for use as a library. 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.
In addition to motor vehicles, bookmobiles have been based on various means of conveyance, including bicycles, boats, and trains, as well as elephants, camels, horses, mules, and donkeys.
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.
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 did not.
Bookmobiles reached their height of popularity in the mid-twentieth century.
Bookmobiles are still in use, operated by libraries, schools, activists, and other organizations. Although some feel the bookmobile is an outmoded service, giving 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 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.
National Bookmobile Day
- In Kenya, the Camel Mobile Library Service is funded by the National Library Service of Kenya and by Book Aid International and it operates in Garissa and Wajir, near the border with Somalia. The service started with three camels in October 1996 and had 12 in 2006, delivering more than 7,000 books —in English, Somali, and Swahili. Masha Hamilton used this service as a background for her 2007 novel The Camel Bookmobile.
- "Donkey Drawn Electro-Communication Library Carts" were being employed in Zimbabwe in 2002 as "a centre for electric and electronic communication: radio, telephone, fax, e-mail, Internet".
- In Indonesia in 2015, Ridwan Sururi and his horse "Luna" started a mobile library called Kudapustaka (meaning "horse library" in Indonesian). The goal is to improve access to books for villagers in a region that has more than 977,000 illiterate adults. The duo travel between villages in central Java with books balanced on Luna's back. Sururi also visits schools three times a week.
- In Thailand in 2002, mobile libraries were taking several unique forms.
- Elephant Libraries were bringing books as well as information technology equipment and services to 46 remote villages in the hills of Northern Thailand. This project was awarded the UNESCO International Literacy Prize for 2002.
- A Floating Library had two book boats, one of which was outfitted with computers.
- A three-car "Library Train for Homeless Children" (parked in a siding near the railway police compound) was a "joint project with the railway police in an initiative to keep homeless children from crime and exploitation by channeling them to more constructive activities". The train was being replicated in "a slum community in Bangkok", where it, too, would include a library car, a classroom car, and a computer and music car.
- Book Houses were shipping containers fitted out as libraries with books. The 10 original Book Houses were so popular, another 20 units were already being planned.
- In Glasgow, Scotland in 2002, MobileMeet—a gathering of about 50 mobile libraries that was held annually by the IFLA—there were "mobiles from Sweden, Holland, Ireland, England, and of course Scotland. There were big vans from Edinburgh and small vans from the Highlands. Many of the vans were proudly carrying awards from previous meets."
- Since 1953, the Libraries of the Community of Madrid, Spain, have operated a bibliobus program with books, DVDs, CDs, and other library materials available for check out.
- A floating library, whose ship's name is "Epos", was begun in 1959 and serves the many small communities on the coast of Western Norway.
- In Estonia, the bookmobile "Katarina Jee  " has been running since 2008, serving patrons in suburbs of Tallinn.
- In Finland, the first mobile library was established in Vantaa in 1913. There are currently about 200 bookmobiles in Finland, operating across the country.
- Street Books is a nonprofit book service founded in 2011 in Portland, Oregon that travels via bicycle-powered cart to lend books to “people living outside”.
- Books on Bikes is a program begun in 2013 by the Seattle Public Library that uses a customized bicycle trailer pulled by pedal power to bring library services to community events in Seattle.
- The Library Cruiser is a "book bike" from the Volusia County Libraries that debuted in Florida in September 2015. It is ridden by library staff to various locations, offering library books for check out, as well as WiFi service, ebook access help, and information on obtaining a library card.