Libraries and Archives (U.S.) — NAICS 51921

An investor's primer for public- and private-market audiences.

Single-child level. In the North American Industry Classification System (NAICS, the U.S. government's standard industry-coding scheme), the five-digit industry 51921 contains exactly one six-digit national industry — 519210, Libraries and Archives. The two codes cover the same activity, the same establishments, and the same money. This page gives the rollup figures for the 51921 level and then points you to the child. For the full analysis — the investable universe, licensing economics, regulation, consolidation, risks, and how to invest — read the 519210 primer.

1. Overview

Libraries and archives collect, organize, preserve, and lend information — books, journals, media, digital content, and historical records — to the public, to students and researchers, and to institutions. [1] The defining fact for an investor is that this is overwhelmingly a public-sector and nonprofit field: the organizations that spend the money are public library districts, state and national archives, and the libraries embedded in universities and public schools. They run on tax appropriations, institutional budgets, and grants, and are measured on usage — visits, circulation, programs — not on earnings.

Consequently there is no listed company that is a library or archive. Investors gain exposure indirectly: in public markets through the "picks-and-shovels" vendors that sell into library budgets (subscription-database and journal publishers, integrated-library-system software, records-storage firms), and in private markets through the privately held pure-play vendors — or, for fixed-income investors, through the municipal bonds that finance library buildings and districts directly. All of that detail lives in the 519210 primer.

2. What's inside — and why this level equals its one child

NAICS is a nested hierarchy: each five-digit industry is subdivided into one or more six-digit national industries. Code 51921 has a single child, 519210, so the subdivision is a formality — the rollup and the leaf are the same population of establishments. There is no aggregation across multiple children to do here, and nothing at the 51921 level that is not also at 519210.

In scope (both codes): public and community libraries; academic and research libraries; school libraries serving kindergarten-through-grade-twelve (K–12) education; special and corporate libraries (law firms, hospitals, museums, companies, agencies); archives of documents, photographs, maps, and audiovisual material, whether physical or electronic; and commercial operators providing digital lending, cataloging, research, and archival services. [1]

Out of scope (adjacent codes, covered in the child): book, periodical, and software publishers (NAICS 5131 / 513210) — a separate industry where much of the profit concentrates; web search portals and other information services (519290); cloud hosting and data processing (518210); and commercial physical records storage / information management (e.g., 561410 / 493190), the code where the largest publicly traded archive-adjacent company, Iron Mountain, actually sits. [1]

3. Size — this level's rollup figures

Because 51921 is identical to 519210, the federal statistics for the two codes are one and the same. Our ground-truth file for this level carries the U.S. Census Bureau Economic Census 2022 concentration series; the figures below are exactly those values (receipts reported in thousands of dollars). [4]

The concentration ratios (CRn = combined revenue share of the n largest firms) and the low Herfindahl-Hirschman Index (HHI, a 0–10,000 scale on which below 1,500 counts as "unconcentrated") show that the commercial slice of this industry is fragmented among many small operators. [4]

Not in this level's file: establishment count, paid-employee count, and payroll are not carried in our 51921 ground-truth data — the child primer sources those from the separate County Business Patterns 2023 release (≈2,326 establishments, ≈25,277 employees, ≈$1.06 billion annual payroll) rather than from this file. No growth rate, profit margin, or capital-expenditure figure is reported at this level either; none is invented here. [3]

Undercount caveat (critical). These figures materially understate the real library-and-archives economy. Federal business statistics capture mainly for-profit, paid-employee operations; they exclude government-operated establishments, most public employees, and the self-employed, and public libraries are specifically an excluded governmental activity. [3][4] Since ownership is dominated by governments and nonprofits, the ~$2.70 billion receipts figure describes only a commercial sliver. Adding the institutional base (public-library operating revenue alone was roughly $14 billion, ~86% from local government, and academic-library operating spend roughly $8 billion) puts the true footprint an order of magnitude higher — well over $22 billion a year before school, special, and federal libraries. That institutional money is what flows outward to the investable vendors. [6][7][8]

4. Investable universe — where value concentrates

Value does not concentrate anywhere within 51921 as a listed asset, because the level is entirely institutional. It concentrates in the suppliers to libraries and in the records-storage business adjacent to them — each a diversified information-services company for which libraries are one segment:

• Listed vendors ("picks and shovels"): RELX (Elsevier, LexisNexis), Clarivate (CLVT — ProQuest, Ex Libris), Thomson Reuters (TRI — Westlaw), John Wiley & Sons (WLY), Springer Nature (Frankfurt: SPG), Iron Mountain (IRM — records storage, adjacent NAICS), and Constellation Software (CSU — owns SirsiDynix). [13][14]
• Private / non-corporate pure-plays: OverDrive (the Libby app, ~90% of library digital lending; owned by KKR), EBSCO, Follett (Francisco Partners), Cengage/Gale, Axiell, Midwest Tape/Hoopla, plus member-owned cooperatives (OCLC, Equinox) and open-source systems (Koha, FOLIO) that cannot be bought. [13][15]
• Direct route to the institutions: municipal general-obligation and library-district bonds — the one way a public-market (fixed-income) investor lends straight to a library.

The full table, ownership detail, and market-share figures are in the 519210 primer.

5. How the money works

Two engines, unchanged from the child. The institutions run on budgets, not profit: a public library's "revenue" is a tax appropriation (~86% local, chiefly property taxes), roughly two-thirds of spending goes to staff, and the operative metrics are cost-per-use (expenditure per capita, cost per visit, cost per circulation), not margin. [7] The vendors earn recurring, high-margin income: multi-year database/journal/software subscriptions with steep switching costs; per-title e-book and audiobook licenses that expire (one-copy/one-user, metered, and cost-per-circulation models); and bond-like physical-archiving storage fees. [16][17] The defining tension — flat public budgets versus above-inflation licensing costs — favors the sell-side. Vendor metrics: annual recurring revenue (ARR), renewal/churn, gross margin, free cash flow, content-rights costs, customer concentration, and leverage.

6. Demand drivers

Local-government fiscal health (sets ~86% of public-library revenue); population, enrollment, and literacy; the digital shift toward e-book and e-audiobook lending (which pulls budgets into licensing); research intensity and the move to open-access publishing; the expanding community-services role (workforce help, digital literacy, broadband); preservation and digitization of aging and born-digital records; and generative artificial intelligence (AI), which both raises demand for authoritative, rights-cleared collections and threatens to substitute for reference and discovery. [6][7][9][20]

7. Regulation

Libraries are not economically regulated like utilities; what matters is funding policy, copyright, connectivity, and access. Key levers: the Institute of Museum and Library Services (IMLS) and the Library Services and Technology Act (LSTA), the only federal program funding libraries exclusively (~$160–180 million/year, and the subject of a live 2025–26 political fight over the agency's survival); copyright's first-sale doctrine and Section 108 (which govern physical lending but not licensed digital content — the legal root of the e-book pricing dispute); E-Rate and the Children's Internet Protection Act (CIPA) for connectivity; the Americans with Disabilities Act (ADA) and the 2024 Department of Justice web-accessibility rule; and federal/state records law for archives. [18][19]

8. Consolidation

Little commercial competition exists on the institutional side (libraries compete for public funding, and against free alternatives like Google, Amazon, and AI chatbots, not against each other). The structural story is vendor consolidation: Clarivate's $5.3 billion ProQuest purchase (2021), Constellation's acquisition of SirsiDynix (2024), Francisco Partners' of Follett (2021), and OverDrive's ~90% grip on library digital lending. Fewer suppliers and expiring licenses steadily raise libraries' input costs — the flip side of what makes the vendors attractive. Open-source systems and cooperatives (Koha, FOLIO, OCLC, Equinox) are the counterweight. [13][15]

9. Risks

Political and funding risk (the IMLS episode; failed local levies; book-access politics); licensing-cost inflation eroding fixed budgets; vendor concentration and single-supplier dependency; unsettled copyright and AI litigation; digital substitution by search engines and generative AI; municipal fiscal stress tied to property-tax cycles; staffing erosion (school-librarian full-time equivalents fell ~25% from 2009–10 to 2022–23); and measurement risk — do not size this industry from the ~$2.70 billion receipts figure, which omits the far larger government and nonprofit base. [3][4][10][16][19]

10. How to invest & outlook

There is no direct equity in 51921 itself. Public-market exposure comes from vendor equities (RELX, CLVT, TRI, WLY, SPG, IRM) — in every case a fraction of a diversified business, to be judged on segment disclosures, renewal rates, pricing power, and cash generation, never benchmarked against the federal NAICS receipts figure — and from municipal bonds for direct, credit-based exposure to the institutions. Private-market exposure runs through private equity, growth equity, private credit, or secondaries into the privately held pure-plays (OverDrive, EBSCO, Follett, Axiell, Midwest Tape).

Outlook: demand for library services looks structurally resilient (record visits, growing digital circulation, expanding community roles), while the durable pressures — licensing-cost inflation and vendor concentration — favor the suppliers over the institutions. Net: a stable, slow-growth, publicly funded field whose profits accrue mainly to a handful of concentrated, largely private vendors. See the 519210 primer for the complete treatment. [6][19]

---

Sources

Federal statistics for this level are from the U.S. Census Bureau Economic Census 2022 concentration series (our ground-truth file for NAICS 51921). All other citations are carried over from the 519210 child primer, to which the reader is referred for full detail.

1. U.S. Census Bureau, 2022 NAICS Manual — NAICS 519210 definition and adjacent-industry cross-references, 2022. https://www.census.gov/naics/reference_files_tools/2022_NAICS_Manual.pdf
2. U.S. Census Bureau, County Business Patterns 2023 (NAICS 519210; via Histometrics ingested federal statistics). https://www.census.gov/programs-surveys/cbp.html
3. U.S. Census Bureau, Economic Census 2022 — Concentration of Largest Firms (NAICS 51921 / 519210; via Histometrics ingested federal statistics — this level's ground truth). https://www.census.gov/programs-surveys/economic-census.html
4. Institute of Museum and Library Services, "Increased Public Library Usage Shown by IMLS Survey Data" (Public Libraries Survey, FY2023), 2025. https://www.imls.gov/research-evaluation/surveys/public-libraries-survey-pls
5. American Academy of Arts & Sciences, Humanities Indicators, "Public Library Revenue, Expenditures, and Funding Sources," 2021. https://www.amacad.org/humanities-indicators/public-life/public-library-revenue-expenditures-and-funding-sources
6. National Center for Education Statistics, Digest of Education Statistics, Table 701.40 (postsecondary library expenditures), 2022. https://nces.ed.gov/programs/digest/d22/tables/dt22_701.40.asp
7. Association of College & Research Libraries / American Library Association, "The State of U.S. Academic Libraries: Findings from the ACRL 2023 Annual Survey," 2024. https://www.ala.org/news/2024/10/state-us-academic-libraries-findings-acrl-2023-annual-survey
8. Education Week, "What the Numbers Say About the Drop in School Librarians," 2023. https://www.edweek.org/teaching-learning/districts-lost-school-librarians-over-the-pandemic/2023/04
9. Marshall Breeding / American Libraries Magazine, "2024 Library Systems Report," 2024. https://americanlibrariesmagazine.org/2024/05/01/2024-library-systems-report/
10. Iron Mountain Inc., FY2024 results (via SEC filings and earnings coverage), 2024–2025. https://www.sec.gov/cgi-bin/browse-edgar?action=getcompany&CIK=0001020569&type=10-K
11. Marshall Breeding, Library Technology Guides, "OverDrive" vendor profile (KKR acquisition; ~90% share; 43,000+ libraries), 2020. https://librarytechnology.org/vendor/overdrive
12. Library Journal, "HarperCollins Puts 26 Loan Cap on Ebook Circulations," 2011. https://www.libraryjournal.com/story/harpercollins-puts-26-loan-cap-on-ebook-circulations
13. The Authors Guild, "E-book Library Pricing: The Game Changes Again," 2019. https://authorsguild.org/blog/e-book-library-pricing-the-game-changes-again/
14. Institute of Museum and Library Services, "Grants to States Overview" (LSTA formula funding), 2024. https://www.imls.gov/grants/grants-state
15. American Library Association, "Court permanently blocks Trump's executive order to dismantle federal agency for America's libraries," 2025–2026. https://www.ala.org/news/2025/11/court-permanently-blocks-trumps-executive-order-dismantle-federal-agency-americas
16. Public Library Association, 2024 Public Library Technology Survey Report, 2024. https://www.ala.org/sites/default/files/2024-07/PLA_Tech_Survey_Report_2024.pdf
17. U.S. House Office of the Law Revision Counsel, 17 U.S.C. §108: Reproduction by Libraries and Archives, 2026. https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim-title17-section108
18. U.S. Department of Justice, ADA.gov, "Fact Sheet: New Rule on the Accessibility of Web Content and Mobile Apps Provided by State and Local Governments," 2024. https://www.ada.gov/resources/2024-03-08-web-rule/
19. Universal Service Administrative Company, "E-Rate" (Schools and Libraries Universal Service Support Program), 2026. https://www.usac.org/e-rate/
20. Follett, "Francisco Partners Acquires Follett School Solutions," 2021. https://www.follettlearning.com/press-release/francisco-partners-acquires-follett-school-solutions/