Crossref is a publisher-run not for profit organization that maintains a database of information about publications that have a Digital Object Identifier (DOI), which includes most publications in peer-reviewed journals, many academic books, conference proceedings, and more. The Crossref API provides a number of ways to query this database. Works can be queried directly by DOI, or by title, publication, editor, and other attributes. Results for an individual publication typically include license information, publication dates, and a detailed bibliography of all cited works. Depending on the publisher, additional data such as funding information may also be present. As is typical for REST APIs, queries are performed by fetching a specially constructed URL and results are returned in JSON format. Alternately, users may access the API using one of the libraries listed on the Libraries section of the Crossref API website.