The 10 Main Dewey Decimal Categories
The ten main classes are a starting point. A precise number depends on the subject and the way a book approaches it.
Computing & general knowledge
Start here for computing and information, libraries, encyclopedias and works that range across many subjects. A general reference book may belong here; a reference book about one particular discipline usually stays with that discipline.
A programming handbook can be classified in the 000s, while a mathematics textbook usually belongs in the 500s.
Catalogue edition examples
- Clean Code — 005.1
- Learning Python — 005.117
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Philosophy & psychology
This class brings together philosophical questions and the study of thinking and behaviour. Topics include logic, ethics, perception, personality and mental processes. Practical books about habits can have psychology numbers even when they are marketed as self-improvement.
Thinking, Fast and Slow has 153.42 in the Harvard record linked from our book page.
Catalogue edition examples
- Thinking, Fast and Slow — 153.42
- Atomic Habits — 155.24
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Religion
Use this broad area to explore religious beliefs, traditions, texts and institutions, as well as arguments about religious ideas. The number describes a subject; it does not endorse a belief. Different traditions have their own subdivisions within the class.
A work about the idea of God can have a different number from a history of a particular religious community.
Catalogue edition examples
- The God Delusion — 211.8
- Mere Christianity — 230
- Educated — 270.092
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Society & social sciences
These numbers cover how people organise societies: economics, politics, law, public services, education and related subjects. The approach matters. An economic study of money is not necessarily classified with a psychological study of decision-making.
The Psychology of Money has 332.4019 in the Harvard edition record used on this site.
Catalogue edition examples
- The Psychology of Money — 332.4019
- Guns, Germs, and Steel — 303.4
- The Anxious Generation — 305.230973
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Language
This area concerns language itself: how languages work, grammar, dictionaries, translation and learning a language. A novel written in French is still literature; its language alone does not move it into the 400s.
A French grammar and a French novel serve different purposes and need not stand together.
Catalogue edition examples
- The Language Instinct — 400
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Science & mathematics
Look here for mathematics and the natural sciences, including astronomy, physics, chemistry, earth science and living organisms. Books that explain a natural process often belong here, while books about applying that knowledge can belong in technology.
Astronomy studies the universe; engineering a spacecraft is a different disciplinary approach.
Catalogue edition examples
- A Brief History of Time — 523.1
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Technology & practical subjects
Technology in this context is broader than computers. It includes medicine, engineering, agriculture, home management and other applications of knowledge. Cooking is a useful reminder that everyday practical subjects belong in the system too.
A cookbook and a scientific study of food chemistry can receive different numbers.
Catalogue edition examples
- Joy of Cooking — 641.5973
- Salt, Fat, Acid, Heat — 641.5
- The Way Things Work Now — 600
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Arts & recreation
This class covers visual and performing arts, music, recreation, games and sports. The focus of a book matters more than its format: a book of photographs, a technical photography manual and a photographer’s life story may not share a precise number.
A history of painting and a guide to drawing are related but more specific than the broad 700 label.
Catalogue edition examples
- The Design of Everyday Things — 745.20019
- Drawing on the Right Side of the Brain — 741.2
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Literature
Literature includes writing as an art and works about it. Form, literary tradition and period can affect a detailed number. Many libraries shelve novels under FIC or an author’s name instead of assigning a numeric Dewey shelf mark.
An English translation of a novel does not automatically become English literature for classification purposes.
Catalogue edition examples
- The Elements of Style — 808.042
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
History & geography
This class covers history, geography and travel, with important distinctions between place, period and subject. Biography is not universally filed under one number: a life can be placed with its subject, and local libraries may use a separate biography collection.
A country’s history and its present-day travel guide can sit in different parts of the 900s.
Catalogue edition examples
- Man’s Search for Meaning — 940.5318092
- Sapiens — 909
These numbers belong to the linked edition records. Compare their sources and your library’s local practice.
Why a topic can cross categories
One topic can be studied through science, history, economics or art. A subject word on its own is not enough to guarantee a unique classification. Compare books that take a similar approach, then check the relevant source record.
Need the short version? Open the one-page chart. Need to read a number? See how Dewey numbers work.