What is FHIR (Fast Healthcare Interoperability Resources)?

FHIR (Fast Healthcare Interoperability Resources)

FHIR (Fast Healthcare Interoperability Resources) is a standard for exchanging healthcare information electronically, published by HL7 International. Data is exchanged as modular components called resources, such as Patient, Observation and Medication, which are combined to solve clinical and administrative problems. FHIR is built on web standards including XML, JSON, HTTP and OAuth.

Resources and how they are exchanged

The resource is FHIR's basic building block: all exchangeable content is defined as a resource. FHIR has resources for administrative concepts such as patient, provider, organization and device, and for clinical concepts such as problems and medications. Specific use cases are usually implemented by combining resources through references.

Each resource carries a human-readable text representation in HTML as a fallback for clinical safety. In exchange, resources can be represented in XML, JSON and Turtle.

HL7 describes FHIR as a RESTful specification. In practice, the core specification supports Level 2 of the REST maturity model, and full Level 3 is possible through extensions. FHIR also supports messaging, documents and other service models, and resources can be used without REST.

Profiles, US Core and SMART App Launch

Base resources can be used as is or adapted for local requirements with profiles, extensions and terminologies. All systems can read all resources; profiles let applications add more control and meaning.

US Core is the HL7 implementation guide that defines the minimum constraints on FHIR R4 resources for US use. Each annual release reflects changes to the US Core Data for Interoperability (USCDI). HL7 says US Core has become the foundation for US Realm FHIR implementation guides.

The SMART App Launch implementation guide defines patterns based on OAuth 2.0 for applications to authorize, authenticate and integrate with FHIR servers. One pattern lets a user-facing app launched from an EHR receive context such as the currently selected patient. Another lets a backend service connect with no user involved.

FHIR and HL7 Version 2

HL7 Version 2 was HL7's first information exchange standard and is one of its most widely adopted, prominent in inpatient settings around the world. It exchanges messages built from reusable segments.

FHIR supports an event-based messaging paradigm similar to Version 2, as well as documents, REST and other service models. HL7 describes FHIR as an evolutionary development path from Version 2 and CDA, with which it can coexist. FHIR can be used as a stand-alone exchange standard or with existing standards.

Versions

FHIR R5 (version 5.0.0), published March 26, 2023, is the current published version. R4 (version 4.0.1, October 30, 2019) was the first release with normative content, and US Core is built on it. FHIR is published as a mixed standard: normative portions are kept stable for implementers, and other parts are still in trial use.

HL7's directory of published versions lists R6 ballots and an R6 snapshot dated July 17, 2026.

FHIR in US health IT certification

In the ONC Health IT Certification Program, criterion § 170.315(g)(10) covers a standardized API for patient and population services. ONC applies the HL7 FHIR US Core Implementation Guide and the FHIR Bulk Data Access standard in certification and testing to this criterion. Developers must publicly document which US Core options their product supports.

Who publishes FHIR

Health Level Seven International (HL7), founded in 1987, is a not-for-profit, ANSI-accredited standards developing organization. Level Seven refers to the application layer of the ISO Open Systems Interconnection model. HL7 dedicates the FHIR specification to the public domain under CC0 1.0.

Sources

Checked November 5, 2026.

Related Terms

HL7EHRDICOMHealthTechInteroperability