The 10 examples of tertiary sources most students meet are encyclopaedias, dictionaries, textbooks, almanacs, handbooks, bibliographies, indexes, databases, atlases and biographical works such as Who’s Who. A tertiary source compiles, organises and summarises information that already exists in primary and secondary sources, giving you a quick, big-picture overview of a topic rather than original evidence or fresh analysis. This guide defines each of the 10 examples, sets tertiary sources against primary and secondary sources in a comparison table, walks through a worked example, and shows you exactly how and when to use them in academic work without leaning on them as your main evidence.
What is a tertiary source?
A tertiary source is an information source that compiles, analyses and synthesises both primary and secondary sources. Tertiary sources provide an overview or summary of a topic, making complex information more accessible and manageable, partly because of our natural cognitive bias to simplify what we read. They sit one step removed from the event or phenomenon under study, because they are built on secondary sources, which are in turn built on primary sources.
In plain terms, a tertiary source is a third-hand account or representation of events and information. It is the map of the territory rather than the territory itself. Be mindful of the actor-observer bias here too: how an event is perceived by those who lived it can differ from how a summary later represents it, so a tertiary entry is always a compressed, second-hand interpretation.
Tertiary sources are most valuable at the start of a project. They orient you, hand you the right keywords, and point you towards the deeper material you will actually cite. Knowing how they differ from the other two tiers is the key to citing the right thing, so the table below sets all three side by side before we list the examples.
Primary vs secondary vs tertiary sources at a glance
| Source type | What it is | Distance from the event | Typical examples | Best use in your work |
|---|---|---|---|---|
| Primary | Original, first-hand material created at the time of the event or study | Closest — the raw record | Diaries, interviews, survey data, photographs, lab results | Direct evidence you analyse yourself |
| Secondary | Analysis or interpretation of primary material | One step removed | Journal articles, monographs, critiques, literature reviews | Scholarly support for your argument |
| Tertiary | Compilation and summary of primary and secondary sources | Two steps removed | Encyclopaedias, textbooks, almanacs, databases | Background, orientation and finding other sources |
For a deeper treatment of the first two tiers, see our guide on the difference between primary and secondary sources. The rest of this article stays firmly in the tertiary lane.
10 examples of tertiary sources
Here are the 10 examples of tertiary sources you are most likely to use, each with a short definition and a note on what it is good for. Together they cover almost every reference work you will reach for in the early days of a project.
1. Encyclopaedias
Both general encyclopaedias, such as the Encyclopaedia Britannica, and specialised ones, such as the Encyclopedia of World History. They summarise what is broadly known about a topic and are the classic example of a tertiary source. Use them to grasp the shape of a subject, then move on to cited scholarship.
2. Dictionaries
General and specialised dictionaries that define and explain terms and concepts. A subject dictionary, such as a dictionary of psychology, is especially useful for pinning down how a field uses a word before you read denser secondary material.
3. Textbooks
Course textbooks synthesise primary and secondary material to give students an overview of a subject. They are sometimes argued to sit between secondary and tertiary, but their compiling, summarising function makes them tertiary in most schemes. Be wary of the Pygmalion effect when a textbook frames a debate as settled, because expectations can quietly shape how you read the evidence.
4. Almanacs
Almanacs contain statistical, factual and current information, refreshed each year. They are an efficient way to grab a verified figure — a population, a date, a record — for quick reference, provided you cite the original data behind the number where it matters.
5. Handbooks and fact books
Such as a handbook on birds or a fact book about countries. These gather established knowledge in a field into one structured volume, which makes them a reliable starting point and a good map of the sub-topics worth exploring further.
6. Bibliographies
Bibliographies list the primary and secondary sources on a particular topic. A bibliography on Shakespeare, for instance, might list the primary works (his plays and poems) and the important secondary analyses (the articles and books that interpret them). They are pure signposts: you read the listed works, not the list.
7. Indexes and abstracts
A periodicals index lists articles from journals and magazines, and abstracts give brief summaries of those articles. These can sometimes reveal publication bias if certain topics are clearly favoured over others. Treat an abstract as a doorway to the full article, never as a substitute for reading it.
8. Databases
Tools such as JSTOR or ProQuest provide access to large numbers of primary and secondary sources, but they are tertiary in their own right because their role is to organise and categorise knowledge. The database is the index; the articles it returns are your real evidence. To search them efficiently, see our walkthrough on using Google Scholar for academic research.
9. Atlases and maps
A single map can be primary or secondary, but many atlases compile various maps and related data, which makes the atlas tertiary. They are ideal for orientation — understanding where, when and in what context something sits — before you turn to specialised geographic or historical scholarship.
10. Biographical works and review articles
Reference works such as Who’s Who give brief details about many people, and review articles summarise the current state of research on a topic. With both, watch for explicit bias in how individuals or findings are presented, and for confirmation bias when a review aligns a little too neatly with what you already believe. Use them to map a debate, then read the cited studies yourself.
Beyond these 10 examples, you will also meet other tertiary formats: directories (lists of people, organisations or institutions, usually with contact details), guides (museum guides, how-to guides and style manuals), and chronologies or timelines (lists of events in chronological order). Each follows the same logic — it compiles and summarises rather than creating new knowledge — so the 10 examples above are a representative core rather than an exhaustive list.
How to tell if a source is tertiary
A tertiary source provides overviews, summaries or generalisations of primary and secondary material, and is usually aimed at a general audience. When you are unsure which tier a source belongs to, run it through these checks.
- Purpose — If the main intent is to organise, index or summarise other sources, it is likely tertiary.
- Content — It compiles the work of others into broad overviews or synthesised data rather than presenting new findings.
- Citations — It may give a general overview without deep references, because its goal is summarisation, not original argument.
- Detail level — It offers a high-level summary rather than nuanced, in-depth analysis.
- Authorship — Experts may write it, but it compiles what is already known rather than presenting their original research.
- Audience — If it is pitched at the public or to newcomers, it is probably tertiary.
These signals also feed into broader source quality. For a full method, our guides on how to evaluate sources and how to find peer-reviewed sources show you how to weigh authority, currency and evidence once you have identified the tier.
Worked example: classifying a source step by step
Theory is easiest to grasp on a concrete case. The box below classifies a single subject — the Battle of Hastings — across all three tiers, then shows how a student would actually use the tertiary one.
How a student uses the tertiary source correctly: read the Britannica entry first to get the date, the key figures and the outline of events; note the names and works it mentions; then track down the cited primary and secondary sources and quote those in the essay. The encyclopaedia gave you the map and the keywords — it does not appear as your main evidence. That is exactly the right role for any of the 10 examples of tertiary sources above.
Tertiary sources across different disciplines
The same 10 examples of tertiary sources look slightly different depending on your field, because every discipline has its own reference works. Recognising the discipline-specific version helps you reach for the right one quickly.
| Discipline | Typical tertiary sources | What you would use it for |
|---|---|---|
| History | Encyclopaedias, chronologies, historical atlases | Establishing dates, sequence of events and context |
| Sciences | Handbooks, review articles, subject databases | Mapping the current state of research before reading the studies |
| Medicine and health | Clinical handbooks, drug compendia, fact books | Quick reference for established, summarised guidance |
| Law | Legal dictionaries, encyclopaedias, indexes | Defining terms and locating the primary statutes and cases |
| Humanities | Biographical dictionaries, bibliographies, companions | Orientation, then a route to the primary texts and criticism |
In every column the principle is identical: the tertiary source organises and summarises, and your real evidence comes from the primary and secondary works it leads you to. A clinical drug compendium, for example, is tertiary because it consolidates and summarises data from primary studies and secondary literature into quick-reference monographs — handy at the bench, but not a substitute for the underlying trials.
Common mistakes students make with tertiary sources
Tertiary sources are easy to use and just as easy to misuse. These are the slips markers notice most often, and each one is simple to avoid once you know the pattern.
- Citing the encyclopaedia instead of the source it cites. Quoting an encyclopaedia or textbook as your evidence signals shallow research. Follow its references to the primary and secondary works and cite those.
- Treating a summary as the whole picture. A tertiary entry compresses a debate into a few lines and can flatten nuance. Read the underlying studies before you claim a question is settled.
- Trusting outdated reference works. An almanac or handbook that is several years old may carry superseded figures. Check the edition date and verify time-sensitive facts against current data.
- Over-relying on a single database. One database reflects one set of editorial choices. Cross-check across more than one, and read our guide on credible source habits to keep your evidence base balanced.
- Ignoring bias in the compilation. Even neutral-looking reference works make selection decisions. Stay alert to which topics, people or findings are emphasised, and corroborate where it matters.
Avoiding these mistakes keeps tertiary sources in their proper supporting role and protects the academic integrity of your work, because every claim that carries weight is traced back to evidence you have actually read.
How and when to use tertiary sources
Used well, tertiary sources save hours of wandering. Used as your main evidence, they weaken an argument. Here is the practical split.
How to use them
- Start your research — Get a broad overview to identify key themes, names, dates and foundational facts.
- Find primary and secondary sources — Let bibliographies, databases and reference lists point you to the deeper material you will cite.
- Grab quick facts and figures — Use almanacs and fact books for a date or statistic, then verify it against the original.
- Understand context — Timelines and atlases place an event in its wider setting.
- Compare at a high level — Review articles and handbooks help you compare theories or methods before you read each in depth.
When to use them
- Preliminary research — To familiarise yourself with the main ideas before going deep.
- When primary or secondary sources are scarce — A summary can bridge a gap while you keep searching.
- Filling knowledge gaps — To shore up your understanding of an unfamiliar area.
- Reference and verification — To double-check a date, name or fact quickly and reliably.
“Tertiary sources are excellent for getting your bearings, but the evidence in a strong piece of academic writing should come from the primary and secondary sources they point you towards.” — ResearchProspect academic team
Cautions
- Tertiary sources give a broad overview, not in-depth analysis, so they should not be relied on alone for comprehensive research.
- Although they aim to be objective, they can carry affinity bias or fall out of date if they are not regularly revised. There is also a tendency towards bias for action: we may trust and act on tertiary sources because they are convenient, even when accuracy demands a check. Good scholarly source practice is to verify a tertiary claim against primary or secondary material whenever it matters.
- Strong, original scholarship typically requires primary and secondary sources for evidence, detail and depth; tertiary sources are the starting point, not the destination.
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