You can keep a huge genealogy library in your own home. You don't need to purchase bookcases or build an addition onto the house. You can keep the entire collection in your computer or even in a handheld Kindle, iPad, or similar device. Actually, you don't have to keep a local copy at all, as the entire collection is available online, and you can retrieve the books of interest at any time. . . .
Digitized old genealogy and family history books: 
Several organizations have been digitizing old genealogy and family history books for several years. The number of available books is still growing daily. Perhaps the largest such collection is available in Archive.org's genealogy collection. Available items include books on surname origins, vital statistics, parish records, census records, passenger lists of vessels, and other historical and biographical documents.
Archive.org
Archive.org never charges for any of its holdings. You are free to read, download, print, and enjoy anything and everything available at Archive.org.
Archive.org, a division of the Internet Archive, is a 501(c)(3) non-profit organization that is building a digital library of Internet sites and other cultural artifacts in digital form. Archive.org receives in-kind and financial donations from a variety of sources, including, but not limited to the following: Alexa Internet, the Kahle/Austin Foundation, the Alfred P. Sloan Foundation, the William and Flora Hewlett Foundation, and you. More than 3 million users access Archive.org every day.
When preparing this article, Archive.org listed 83,947 items in its genealogy collection. That number grows every day or so and may be a bit larger by the time you read these words.
The images included in this article were taken from one of the genealogy books in Archive.org's collection. These images serve as typical examples of the items you can retrieve from Archive.org.
Many of the items were scanned at Archive.org's headquarters in San Francisco, but these are supplemented by digitization projects of several other participating organizations, including the following: the Allen County Public Library Genealogy Center in Fort Wayne, Indiana; the Robarts Library at the University of Toronto; the University of Illinois Urbana-Champaign Library; Brigham Young University in Provo, Utah; the National Library of Scotland; the Indianapolis City Library's Indianapolis City Directory and Yearbooks Collection; The Leo Baeck Institute Archives of German-speaking Jewry, Leo Baeck Institute Archives; and the Boston Public Library.
The books and other items are presented exactly as they were printed or written–without any additional indexes. For instance, images of census records are available although you cannot simply enter a name to search for a single entry. You can only search census records by finding the town or city of interest in the printed index, and then manually "turn the pages" of the images with a mouse-click as you look at the records, page by page.
You can view the book images on your computer's screen or download the files in PDF format, EPUB format (used on many ebook readers, including iPad and Android tablets), Kindle format, and several other formats as well. Files may be downloaded using HTTPS secure file transfers, commonly used in many web sites as well as by Torrent downloads, which are more efficient and place much less of a load on Archive.org's servers. Once you have downloaded and saved the file(s), you can keep them as long as you wish and read them at any time on your computer's or ebook reader's screen. Should you wish to do so, you can even print the books on your local printer. I would never waste that much paper when I can already read the books on-screen but I do realize that some people will do so.
The Archive.org genealogy collection is divided into several sub-collections, including:
United States Census – 23,609 items
All images of all U.S. Census records
Compiled records of military units in volunteer Confederate organizations – 536 items
Collection of compiled records showing service of military units in volunteer Confederate organizations.
Compiled records of military units in volunteer Union organizations – 225 items
Collection of compiled records showing service of military units in volunteer Union organizations.
Eastern Cherokee applications of the U.S. Court of Claims – 347 items
Collection of Eastern Cherokee applications of the U.S. Court of Claims.
Family Genealogy – 2,203 items
A collection of family genealogies.
Passenger and Crew Vessel Lists for New York, NY 1897-1957 – 7,126 items
Passenger and Crew lists for vessels arriving in New York, New York 1897-1957.
Passenger Lists of Vessels for Baltimore and Philadelphia – 634 items
Passenger lists of vessels arriving at Baltimore and Philadelphia.
Passengers arriving in the St. Albans, VT District – 1,026 items
Collection of passengers arriving in the St. Albans, VT District.
Passport Applications, 1795-1905 – 695 items
Passport applications from 1795-1905. Microfilm contributed by Allen County Public Library Genealogy Center.
Records of the field offices for the Bureau of Refugees, Freedmen, and Abandoned Lands – 450 items
Records relating to War of 1812 – 456 items
Registers of Births (does not include U.S. Census) – 3,553 items
Veterans Administration Pension Payment Cards – Microfilm – 2,544 items
This is the collection page for the Veterans Administration Pension Payment Cards.
United States Commission to the Five Civilized Tribes – 493 items
Collection of documents from United States Commission to the Five Civilized Tribes.
War Records – 44 items
Collection of lists of soldiers and participants in American wars.
Archive.org may be found at http://www.archive.org although a more direct link to the genealogy and local history collection may be found at https://archive.org/details/genealogy.