Controlled digital lending (CDL) is a model by which libraries digitize materials in their collection and make them available for lending. It is based on interpretations of the United States copyright principles of fair use and copyright exhaustion.
Proponents argue that CDL is legal under those principles because it relies on digital rights management (DRM) to ensure that any library-owned digitized work that is in copyright is loaned for a limited period of time, and that a one-to-one ratio of owned copies to borrowers is maintained. However, opponents have criticized this interpretation, arguing that CDL involves copying, not mere lending, and that a library's purchase of a physical book does not entitle it to produce and lend an e-book or distribute digital copies.
A precursor to CDL was the "Digitize and Lend" program begun in 2011 by the Open Library, a program of the Internet Archive. Also in 2011, the basic principles of CDL were articulated by Michelle Wu in her paper Building a Collaborative Digital Collection: A Necessary Evolution in Libraries. The use of the term "Controlled Digital Lending" to refer to this concept first appeared in the Position Statement on Controlled Digital Lending, published in 2018 alongside a white paper explaining their legal arguments.
CDL is increasingly being considered by a number of libraries and is being followed by library organizations across the United States as well as in other countries. Brazilian experts have argued that the CDL can be applied in the country through a systematic interpretation of cultural rights that extrinsically limits copyright. The Internet Archive has gathered together 12 stories from their blog about libraries that are engaged in aspects of CDL. Lisa Petrides argues that in terms of school libraries, CDL is a positive step forward, but does not go far enough.
In May 2021, the International Federation of Library Associations and Institutions (IFLA) stated that "there is a strong socio-economic case" for CDL; that CDL respects "a number of desirable and widely-recognised principles [...] (libraries’ ability to freely acquire and lend, the technological neutrality of law, the possibility to combine exceptions)"; that CDL's legal basis supports the wider public interest.
One of the core activities of a library is to loan materials, and proponents argue that CDL is a modern digital extension of this function. With CDL, a library takes a physical copy of a legally acquired item and digitizes it. After digitization, DRM is applied to the digital version, and the physical item is then made unavailable for loan. The library catalog record is usually the mechanism to give access to the digital loan, so the record is changed to point to the repository where the digital copy resides. In this way, there is only one copy being loaned for each copy owned by the library. After the loan expires, the DRM software removes the previous borrower's access and the book is available for loan to another patron.
Opponents of CDL argue that CDL is not like lending, which does not require copying, and dispute the claim that only one copy at a time is available for reading. Opponents say that CDL involves first making an unauthorized digital copy of a printed edition of a work, and then making an additional unauthorized digital copy for each "borrower". Opponents also argue that unencrypted digital copies are distributed for viewing in a Web browser, and that these copies can be retained, viewed, or printed from the browser cache even after the e-book is marked as "returned" and is available for "lending" to other readers.
Authors' and publishers' groups have questioned the copyright interpretations that underlie CDL. In early 2019, the National Writers Union and a coalition of forty national and international organizations and federations of writers, photographers, visual artists, translators, publishers, and reproduction rights organizations released a statement entitled "Appeal from the victims of Controlled Digital Lending (CDL)"  that claimed that CDL "violates the economic and moral rights of authors."
In a news article in Publishers Weekly The American Association of Publishers is quoted as stating that CDL "'denigrates' the incentive copyright provides for authors and publishers." The Authors Guild relies on the case of Capitol Records, LLC v. ReDigi Inc., which established that ReDigi could not resell digital music, to argue that libraries would similarly be prohibited from loaning digitized version of books that were legally purchased, and argues that CDL results in lost sales.
Various scholars have framed the Capitol Records, LLC v. ReDigi Inc. as leaving room for CDL as part of a library's non-profit, educational mission. For example, the opinion, authored by Judge Pierre N. Leval, found ReDigi had no actual control of the digital music being sold (licensed iTunes mp3's) and that ReDigi “made reproductions of Plaintiffs’ works for the purpose of resale in competition with the Plaintiffs’ market for the sale of their sound recordings.” Various scholars have pointed out that libraries are not selling works in direct competition with publishers, like the Defendant in ReDigi. Libraries are purchasing books from the marketplace in order to loan the books to their patrons. Additionally Judge Pierre N. Leval, also the originator of the doctrine of transformative fair use, explained in the opinion that a use can be transformative when it “utilizes technology to achieve the transformative purpose of improving delivery of content without unreasonably encroaching on the commercial entitlements of the rights holder.” Again, analyzing this language from the case, some scholars have asserted that CDL does not unreasonably encroach the market for these books any differently than the legal uses already permitted by the copyright law when libraries loan books physically. 
- Wu, Michelle M. (2011). "Building a Collaborative Digital Collection: A Necessary Evolution in Libraries" (PDF). Law Library Journal. 103 (4): 527–551. 2011-34. Archived from the original (PDF) on 2015-10-30. Retrieved 2019-08-02.
- Bailey, Lila; Courtney, Kyle K.; Hansen, David; Minow, Mary; Schultz, Jason; Wu, Michelle (September 2018). "Position Statement on Controlled Digital Lending - Statement on Controlled Digital Lending by Libraries". Controlled Digital Lending by Libraries. Archived from the original on 2019-08-02. Retrieved 2019-08-02.
- Hansen, David R.; Courtney, Kyle K. (2018). "A White Paper on Controlled Digital Lending of Library Books". Controlled Digital Lending by Libraries. Archived from the original on 2019-08-02. Retrieved 2019-08-02.
- Enis, Matt. "Controlled Digital Lending Concept Gains Ground". Library Journal. Archived from the original on 2019-12-04. Retrieved 2019-12-04.
- Price, Gary. "Controlled Digital Lending in Canada: "Protecting Unique Canadiana Works" at the Hamilton Public Library". Infodocket. Library Journal. Archived from the original on 2019-12-05. Retrieved 2019-12-05.
- Mounce, Ross. "A new digitisation opportunity for UK university presses". Research Libraries UK. Archived from the original on 2019-12-05. Retrieved 2019-12-05.
- Couto, Walter Eler do; Ferreira, Sueli Mara Soares Pinto (2020-12-23). "Empréstimo Digital Controlado e direitos autorais no Brasil: algumas reflexões iniciais". Liinc em Revista. 16 (2): e5378. doi:10.18617/liinc.v16i2.5378.
- Adams, Caralee; Bailey, Lila; Freeland, Chris. "Transforming Our Libraries: 12 Stories About Controlled Digital Lending" (PDF). controlleddigitallending.org. Archived (PDF) from the original on 2019-12-05. Retrieved 2019-12-05.
- Petrides, Lisa. "Why Controlled Digital Lending Matters to Schools". ISKME. Archived from the original on 2019-12-05. Retrieved 2019-12-05.
- "IFLA Statement on Controlled Digital Lending". IFLA. 2021-06-22. Retrieved 2021-08-03.
- "Controlled Digital Lending: an Interview with Jonathan Band". International Federation of Library Associations. Archived from the original on 2019-12-04. Retrieved 2019-12-04.
- National Writers Union; et al. "FAQ on Controlled Digital Lending (CDL)". National Writers Union.
- McKay, John, ed. (2019-02-04). "Statement on Flawed Theory of "Controlled Digital Lending"". Association of American Publishers (AAP). Archived from the original on 2019-08-02. Retrieved 2019-08-02.
- "Appeal from the victims of Controlled Digital Lending (CDL)". National Writers Union. Retrieved 2019-12-04.
- "Publisher, Author Groups Protest Library Book Scanning Program". Publishers Weekly. Archived from the original on 2019-12-04. Retrieved 2019-12-04.
- Hruska, Joel. "The Authors Guild Declares War on Digital Library Lending, Libraries". ExtremeTech. Archived from the original on 2019-12-05. Retrieved 2019-12-05.
- Wu, Michelle M. (2019). "Revisiting Controlled Digital Lending Post-ReDigi". First Monday. 24 (5). Retrieved 2020-02-11.
- Courtney, Kyle K. (2020). "Libraries Do Not Need Permission To Lend Books: Fair Use, First Sale, and the Fallacy of Licensing Culture". Medium. Retrieved 2020-02-11.
- Hansen, David R.; Courtney, Kyle K. (2020). "Fair Use, Innovation, and Controlled Digital Lending". Fair Use Week Blog. Retrieved 2020-02-11.
- McCleskey, Sarah E.; Selby, Courtney (2018). "Tried and True: Fair Use Tales for the Telling". Journal of Copyright in Education & Librarianship. 3 (1). doi:10.2139/ssrn.3256427. SSRN 3256427.
- Peterson-Lugo, Billie. "Tech Talk" (PDF). Library Instruction Round Table News. American Library Association. pp. 9, 22–28. Retrieved 2019-12-05.
- Sheppard, Adrian; Bailey, Lila; Katz, Ariel; Mills, Andrea; Slaght, Graeme (2018-05-31). Controlled Digital Lending (CDL): A Panel to Discuss Legal and Practical Considerations Involved in the Implementation of CDL by Public and Post-Secondary Libraries in Canada. ABC Copyright Conference 2018. Harbour Centre, Vancouver: Simon Fraser University (SFU). Retrieved 2019-08-02.
- Wu, Michelle M. (2016-09-12). "Collaborative Academic Library Digital Collections Post-Cambridge University Press, HathiTrust and Google Decisions on Fair Use". Journal of Copyright in Education & Librarianship. 1 (1). doi:10.17161/jcel.v1i1.5921.
- Wu, Michelle M. (2019-02-04). "Revisiting Controlled Digital Lending Post-ReDigi". First Monday. 24 (5). doi:10.2139/ssrn.3328897. S2CID 219360414. SSRN 3328897 – via SSRN Electronic Journal.
- Wu, Michelle M. (2019-07-03). "Shared Collection Development, Digitization, and Owned Digital Collections". Collection Management. 44 (2–4): 131–145. doi:10.1080/01462679.2019.1566107. S2CID 218574586.
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