Using Subjects

A catalog with millions of books may be difficult to search one by one in order to find certain ones, related ones, or to obtain a bird's eye view of the structure of what's available. In addition to indexing basic metadata like title, author, and date, libraries have tried to increase the granularity of book discovery by developing shared taxonomies (organized information hierarchies) with common vocabulary to describe books, as well as classification systems which assign these taxonomies to items, as well as label items with identifiers or labels to enable sorting and efficient retrieval. The Dewey Decimal system and the Library of Congress classification system are two examples.

Circa 2010, the Open Library introduced a Subject System for associating works with lists of free-form, descriptive labels about the book. This idea takes inspiration from library classification systems and is complimentary to book websites like archiveofourown.org and thestorygraph.com. This system was originally [perhaps contentiously] called the "Subject" system.

While, in librarian lingo, "subject" may refer distinctly to the main topic(s) of a book (e.g. "Friendship", "Heartache", "Persecution"), the Open Library team seemed inclined to draw more literally from the linguistic, grammatical definition of "subject", referring more broadly to any things, persons, places, ideas, themes, genres (nouns) relating to the work.

Open Library has historically considered subjects to be people or places, things, ideas, or times. Subjects can be real, like Napoleon or imagined, like Narnia. If we find a match, Open Library will automatically attach subjects to books based on the Library of Congress Subject Headings (LCSH), and anyone who adds or edits a book can add more subjects. Subjects can also be added to authors.

An Example

As of 2024-12, for example, the work "The Psychology of Money" has the labels: "Money", "Quality of Life", "Accounting", "Investing", etc:

As of 2024-12, more than 3M of such labels are associated with works within the Open Library system.

Search by Subject

You can look for works related to specific subjects by visiting the Subjects page. You can also search from any page by entering "subject:" prior to your keyword or phrase in the search field at the top and bottom of any page, like "subject:Fathers and daughters" or "subject:mayors in fiction." Finally, you can also search by subject using the advanced search fields available by clicking "More search options" under the basic search field on any page and entering your query under "Subject."

The Subject Page

When viewing works about subjects on the Subject page, there's a lot of information available to you so you can explore books and subjects thoroughly.

We'll present the covers of all the works related to a Subject in Open Library in the top panel, twelve at a time. You can load more covers by using the arrow buttons to the right, and navigate covers using the same buttons. You can also flip back and forth between all books, or only those books available online to read right now (ebooks).

Below the presentation of covers, an interactive graph displaying the publishing history of works about your selected subject allows you to zoom in on specific periods or single years, and the covers panel will repopulate with the works published in your selected time period. You can reset the chart to its original scale by clicking "Show all" above the covers, or "Reset chart" above the chart.

The next section shows subjects related to the subject you're already exploring. These are provided by looking at the works related to your subject, and seeing what other subjects are related to those. You may also search within a subject, so if you're looking for a book about incunabula, maybe you want to know if it's also related to Venice, and is about the 16th century.