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Reference Work  ·  Vol. IX  ·  January 2026 Two Tiers  ·  One Archive

A Reference Work for World History

Pricing — Free vs. Pro

18,000+ encyclopedia entries live on the free tier. Pro unlocks 60,000+ indexed primary-source documents and one-click citation exports in Chicago, MLA, and APA — built for the deadline that starts in forty minutes.

78,400+ entries 60,200+ primary sources 2.1M citations exported

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The Decision

Two tiers. One archive. Pick the depth you need tonight.

Both tiers draw from the same editorial board of 41 credentialed historians, archaeologists, and classicists. The difference is how deep into the archive you can go — and whether you leave with a citation ready to paste into your bibliography.

Free

The Open Reference

$0/ always

For the curious reader and the late-night essay that needs a defensible answer, fast.

  • 18,000+ encyclopedia entries across world history
  • 312 civilizations and regions covered in the open layer
  • Inline citations and source links on every entry
  • Interactive comparative timeline (read-only)
  • Bookmarking and reading history across devices
  • Primary-source documents (Pro only)
  • Chicago / MLA / APA citation export (Pro only)
  • Confidence ratings on every claim (Pro only)
Start Exploring Free

No card. No trial countdown. The free tier has been free since 2017.

Pro

The Citation-Grade Archive

$8/ month, billed annually

For students writing defensible essays, exams, and research papers under deadline.

  • Everything in Free, including the 18,000+ open entries
  • 60,000+ primary-source documents with full-text search
  • Citation export in Chicago, MLA, and APA — copy, paste, defend
  • Confidence rating on every entry, sourced from the editorial board
  • Interactive timeline with overlay, comparison, and export
  • Offline reading list and printable entry packets
  • Educator tools: shareable reading lists and syllabus exports
  • Priority email support from the editorial team
Start 7-Day Pro Trial

No card to start. Cancel anytime in two clicks from your account.

What Pro Actually Does at 11:47 PM

Citation exports, at the moment you need them most.

The Pro tier was built around a single moment: the student who has twenty-three minutes to assemble a bibliography in a style their professor actually checks. Three things happen, in order.

  1. 01

    Pick the style. Chicago, MLA, or APA — formatted to the current edition.

    Every entry exposes an Export panel with the three formats AP World History, MLA-track humanities seminars, and APA-track social-science courses actually require. Footnotes, parenthetical citations, and "Works Cited" / "References" lists are generated from the same source list — no re-keying between drafts.

    Pro has processed 2.1 million citation exports since launch, with a 94.6% export-success rate across the trailing twelve months. The remaining 5.4% are typically malformed source titles caught by our editorial linter before they reach your bibliography.

  2. 02

    Copy. Paste. Defend the source in the next office hour.

    Each exported citation carries the inline source list as it appeared in the entry — author, work, date, repository, and the confidence rating our editors assigned. If a professor asks "where did you get this?", the answer is the footnote, not a guess. Citations are editable in-line so you can drop in a page number from your own reading without leaving the export panel.

    Every Pro entry is cross-referenced against at least three primary or peer-reviewed sources, verified by the editorial board of 41 historians, archaeologists, and classicists.

  3. 03

    Build a working bibliography across an entire essay, in one pass.

    The reading cart holds entries as you research. At the end of the session, export the whole cart as a single formatted bibliography — Chicago author-date, MLA 9th, or APA 7th — or split it by section for thesis chapters. The cart syncs across desktop and mobile so a citation you flag on a phone is waiting on the laptop when you sit down to write.

    Subscribers report an average query-to-defensible-answer time of 47 seconds, benchmarked against Wikipedia and three competing reference sites in our 2024 internal study.

By the Numbers

The figures behind the archive.

78,400+

Encyclopedia entries hosted as of January 2026, across 312 civilizations and regions.

60,200+

Primary-source documents indexed, transcribed, and citation-ready on Pro.

2.1M

Citation exports processed since launch, in Chicago, MLA, and APA.

4,200+

Years of recorded history covered, from the Olmec to the Ottoman reforms.

Cited in 740+ secondary and post-secondary course syllabi across 28 countries. Featured by Smithsonian Magazine as "the most citation-friendly history reference online" in its March 2024 issue.

From the Classroom

“I assign HistoryKB alongside the print reader in my AP World History sections. The Pro citation export is the part my students actually use — they arrive at office hours with a real bibliography, and we can spend the hour arguing interpretation instead of hunting for a footnote. It is the only reference site I have endorsed to other teachers without a caveat.”

Dr. Helena Marchetti AP World History · Chair, Social Studies Department, Brookline Public Schools HistoryKB educator subscriber since 2021

HistoryKB is cited in 740+ high school and university courses across 28 countries, including AP World History teacher syllabi. We do not claim partnerships with universities — we are cited in their reading lists.

Before You Subscribe

Questions students and teachers actually ask before upgrading.

Do I need a credit card to start the Pro trial?
No. The 7-day Pro trial starts on your account without a card on file. If you choose to continue, you will be prompted for payment on day eight. If you do nothing, your account reverts to the free tier and your reading cart, bookmarks, and exported citations remain intact.
Which citation formats does Pro actually cover?
Chicago author-date and notes-bibliography (current edition), MLA 9th edition, and APA 7th edition. Footnotes, parenthetical citations, and full bibliography lists are all generated from the same source list per entry. Pro has processed 2.1 million citation exports since launch with a 94.6% export-success rate across the trailing twelve months.
How do I cancel, and what happens to my exports?
Cancellation is two clicks from your account page: Settings, then Subscription. There is no retention call, no save-offer pop-up, and no email loop. Your Pro exports — bibliographies, reading lists, annotated entries — remain downloadable from your account as a single archive file for ninety days after cancellation.
Is Pro approved for classroom and syllabus use?
Pro is cited in 740+ secondary and post-secondary course syllabi across 28 countries, including AP World History reading lists. HistoryKB does not assert institutional partnerships unless explicitly verified — we say "cited in syllabi" because that is the verifiable claim. Educator accounts include shareable reading lists and a syllabus export tool. Note: HistoryKB does not host AI-generated content as authoritative; every entry is reviewed by credentialed historians on our editorial board before publication.

Still weighing it? The free tier has been free since 2017. 78,400+ entries are waiting for you there.

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