The ORCID API allows developers to integrate ORCID identifier services into their applications. It uses OAuth2 for authentication and provides a RESTful interface for retrieving and updating ORCID profile and activity record data. Developers can build tools that authenticate users via their ORCID ID, push citations and other works to ORCID records, and provide insights into researcher impact by linking datasets to ORCID profiles. Several existing tools demonstrate uses of the ORCID API such as allowing user profile linking, citation importing, and research analytics services.