# Indexes Overview

Indexes are the bibliographic indexes and registries (like Crossref or PubMed) that list works. A work can be listed in several indexes at once.

## Values

| ID | Display name |
|----|-------------|
| `crossref` | Crossref |
| `datacite` | DataCite |
| `arxiv` | arXiv |
| `doaj` | DOAJ |
| `pubmed` | PubMed |

Use these values with the `indexed_in` filter on works: `filter=indexed_in:doaj`

Like other entities, each index has its own record with live counts — for example, [`/indexes/doaj`](https://api.openalex.org/indexes/doaj) — and the full list is at [`/indexes`](https://api.openalex.org/indexes).