Fields
A field is the second level of OpenAlex’s four-level classification hierarchy: 4 domains → 26 fields → 252 subfields → 4,516 topics. The 26 fields are broad disciplines — “Medicine,” “Computer Science,” “Arts and Humanities,” “Physics and Astronomy,” and so on — each sitting under one of the four domains and gathering a set of subfields beneath it. A field’s OpenAlex ID is a bare number, e.g. 27 for Medicine; fetch one at api.openalex.org/fields/27. Fields are one of several aboutness signals — high familiarity, coarse granularity — see that page to choose the right level for your question.
How it’s made
Fields aren’t classified on their own — they’re a level of the same hierarchy topics are built from. Each of the ~4,500 topics maps up through a subfield to one of the 26 fields, following Scopus’s ASJC categories, and a work “belongs to” a field through the topics assigned to it. The 26 field labels are standardized, but a work lands in one only because a machine-learning model inferred its topic from the work’s text — which is why fields, like the rest of the hierarchy, live under Aboutness rather than Vocabulary. See Topics → How we build it for the full pipeline.
A work’s primary field is the field of its primary_topic. To find works in a field, filter Works by topics.field.id (any assigned topic’s field) or primary_topic.field.id (the primary only). One level up is a domain; one level down is a set of subfields.
Attributes
This is the canonical dictionary of every attribute on a field object. (Confusingly, “field” is both the entity and the generic word for an object’s properties; the properties are dictionaried below.) Attributes shared with other entities (id, ids, display_name, works_count, cited_by_count, created_date, updated_date) are documented once on Common attributes; field-specific notes are below.
id
String. The OpenAlex ID for this field, e.g. https://openalex.org/fields/27. Fields use a bare numeric ID (two digits, 11–36), not the letter-prefixed scheme. See Common attributes.
ids
Object. External identifiers for this field, as URIs: openalex, plus wikidata and wikipedia where a matching article exists.
display_name
String. The field’s name, e.g. “Medicine.” See Common attributes.
display_name_alternatives
List. Other names the field is known by (e.g. “healthcare sciences” for Medicine), for matching and search.
description
String. A short description of what the field covers.
domain
Object. The domain this field belongs to (id, display_name) — the level directly above it in the hierarchy.
subfields
List. The subfields that belong to this field (id, display_name) — the level directly below it.
siblings
List. The other 25 fields (id, display_name), for navigating laterally across the classification.
works_count
Integer. How many works fall in this field (through their assigned topics). See Common attributes.
cited_by_count
Integer. Total citations across all works in this field. See Common attributes.
works_api_url
String. A ready-made Works API URL for every work in this field, e.g. https://api.openalex.org/works?filter=topics.field.id:27. A convenience link; work IDs aren’t stored on the field object.
created_date
String. The date this field was added to OpenAlex (YYYY-MM-DD). See Common attributes.
updated_date
String. The ISO 8601 UTC timestamp of the last change to the field object. See Common attributes.
In the API
The Fields endpoint is at api.openalex.org/fields. Fetch a single field by ID — /fields/27 — or a list, and filter, search, sort, group, and page over it. With only 26 fields, one unfiltered request returns them all.
You can filter and group fields by domain.id and subfields.id, and by works_count, cited_by_count, id, and display_name, all of which also sort. Full-text matching uses the search parameter (the older display_name.search filter is deprecated). To find works in a field, use the Works endpoint: filter=primary_topic.field.id:27 (primary only) or filter=topics.field.id:27 (any assigned topic). See the Fields API reference and the endpoints index.