Free, real,
and worth
your time.
Libraries, archives, data sets and tools worth knowing, chosen by the people who research our lessons. Every one is free; nearly all are run by a library, a university, a public body or a long-standing non-profit, and the few that are companies are marked on their card. Every link goes straight to the source. No affiliate links, no sign-ups to read.
Six shelves
Books and texts
Whole libraries,
free to read.
Public-domain books, scanned collections and reference works that a serious reader can live in. All free; most need no account.
Project Gutenberg
Tens of thousands of public-domain books as plain text, EPUB and Kindle files. Search by author, then pick the EPUB; it reads well on a phone and costs nothing.
Internet Archive
Scanned books, old films, radio, software and the Wayback Machine for pages that have vanished. Use the full-text search to find a phrase inside millions of books at once.
Open Library
A catalogue page for every book, with links to read or borrow scanned copies. Good for finding which edition of an old book you are actually looking at.
Stanford Encyclopedia of Philosophy
Long, peer-reviewed entries on philosophers and ideas, kept up to date by named scholars. Read the first section of an entry for the plain summary before the detail.
Poetry Foundation
Thousands of poems with short notes on the poets. Browse by subject or period when you want a poem for a lesson and do not yet know which one.
Wikipedia
A starting point, never a final source. Read the article, then follow its footnotes to the primary document and cite that. The talk page shows you where a subject is disputed.
Pictures, maps and art
Images you
may use.
Museums, libraries and NASA have put enormous collections online, many of them free to reuse. Check the licence line on each file; open access is not always public domain.
Wikimedia Commons
Over a hundred million freely licensed files. Every file page states its licence and how to credit it; copy that line exactly when you reuse the image.
Library of Congress digital collections
Photographs, maps, manuscripts, newspapers and recordings from the largest library in the world. Filter by "available online", then read the rights note on each item before you reuse it.
NASA Image and Video Library
NASA's photographs, video and audio in one searchable place, most of it free to use with a credit. Search a mission name, then download the largest size available.
Smithsonian Open Access
Millions of images and 3D models from the Smithsonian's museums, released for any use. Look for the "CC0" mark on an item; those need no permission at all.
The Met Collection
The Metropolitan Museum of Art's collection online. Tick "Open Access" in the search filters to see only the works you may download and reuse freely.
David Rumsey Map Collection
Historical maps scanned at very high resolution. Use the viewer to zoom into a single street on a map from 1850; many maps can be laid over a modern one.
New York Public Library Digital Collections
Prints, photographs, maps and manuscripts from the NYPL. The public-domain filter shows what you can download at full size without asking anyone.
Europeana
Objects from thousands of European museums, libraries and archives in one search. Use the reuse filter to keep only what is free to reuse.
Wellcome Collection
A free museum and library in London about health and the human body, with a large open image collection. Strong on the history of medicine.
Science and data
Numbers from
the source.
Where we go when a lesson needs a figure. Each of these shows where its numbers come from, which is the only kind of number we use.
Our World in Data
Charts and explainers on poverty, health, energy, population and more, each one naming its source and letting you download the data. The best first stop for a big-picture number.
World Bank Open Data
Country-level indicators going back decades: population, GDP, life expectancy, electricity access. Search an indicator, pick the countries, download the table.
arXiv
Preprints in physics, mathematics, computer science and more, free to read. Remember that a preprint has not yet been peer reviewed; say so if you cite one.
PubMed
The index of biomedical research from the US National Library of Medicine. Abstracts are always free; the "free full text" filter finds the papers you can read whole.
PhET Interactive Simulations
Free simulations from the University of Colorado Boulder for physics, chemistry, maths, earth science and biology. They run in the browser; try one before you explain the idea in words.
Biodiversity Heritage Library
Scanned natural-history books and journals going back centuries, with the illustrations. Search a species name to find how it was first described and drawn.
Courses and practice
Learn it,
for free.
Where our sixty seconds should send you next. Full courses, textbooks and tools, free to use; some offer an optional account to save your progress.
Khan Academy
Free courses from early maths to advanced science, economics and history, with practice questions. You can watch without an account; sign in only if you want your progress kept.
MIT OpenCourseWare
Lecture notes, problem sets, exams and often full lecture video from MIT courses, free and without registration. Start with a course's syllabus page to see what it assumes you know.
OpenStax
Peer-reviewed, openly licensed textbooks from Rice University, free online and as PDF. Physics, biology, history, economics and more, written for actual courses.
Desmos graphing calculator
Type an equation and see the graph move as you change it. Add a slider to a constant to watch what it does; it is the fastest way to understand a function.
GeoGebra
Geometry, algebra and 3D graphing in the browser, with a large library of classroom activities other teachers have shared. Good for showing a proof move.
Scratch
A free, visual way to learn programming by snapping blocks together, from MIT, aimed at ages eight and up. Make something move in ten minutes; the ideas carry into real languages later.
Code.org
Free computer-science courses and one-hour activities for schools, with teacher materials. The "Hour of Code" tutorials need no setup at all.
Primary sources and archives
The document,
not a summary.
Our rule is two sources per claim, one of them primary. These are where the primary ones live: treaties, laws, letters and records, as written.
United Nations Treaty Collection
The registered text of international treaties, including the Indus Waters Treaty our sample lesson is built on. Search by title, then open the PDF of the original.
The Avalon Project, Yale Law School
Documents in law, history and diplomacy from antiquity to the twenty-first century, as plain text. Fast to search and easy to quote exactly.
US National Archives Catalog
Records of the United States government, with millions of pages scanned: census sheets, photographs, letters, court files. Search a name or a place and filter to items available online.
The National Archives (UK)
A thousand years of British government records, with research guides that explain what a record is before you open it. Some digitised records are free to download; others carry a small fee, stated before you order.
Gallica, Bibliothèque nationale de France
The French national library's digital collection: books, manuscripts, maps, newspapers and prints, much of it in the public domain. Strong on anything touching France and its former empire.
Digital Public Library of America
One search across the digital collections of American libraries, archives and museums. Each result links back to the institution that holds the original.
Sound and voice
Recordings you
may use.
For the ear: audiobooks read by volunteers, and sound and music under open licences for your own projects.
LibriVox
Public-domain books read aloud by volunteers and released free. Quality varies by reader, so sample the first chapter; the catalogue lists several readings of the famous books.
Freesound
Hundreds of thousands of sound recordings and effects under Creative Commons licences. Check each sound's licence; some need a credit and a few do not allow commercial use.
Free Music Archive
Music under open licences, searchable by genre and by what the licence allows. Read the licence line before you put a track under a film.
A note on rights
Free to read is not
free to reuse.
Public domain means no one owns it any more; you may do anything with it. CC0 means the owner has given up every right; treat it the same way. Other Creative Commons licences let you reuse the work on conditions, usually a credit, sometimes no commercial use, sometimes no changes. Open access means you can read it, and says nothing by itself about reuse.
Each site above states its own terms on every item. Read that line, copy the credit as written, and when in doubt, write to the institution; they answer more often than people expect.
Subscribe
New lessons, and
new shelves.
One email when a lesson is published, with the script and the sources inside. When this list grows, we say so in the same email. Nothing else.