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This documentation is under active development and may be incomplete or in some cases incorrect.
The official FHIR specification is the only source of truth: https://hl7.org/fhir/. This section is a practical guide to get you productive quickly. We deliberately focus on certain parts of the spec that are widely used and understood.

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What is FHIR?

At its core, FHIR (Fast Healthcare Interoperability Resources) is a standard way to represent healthcare data as resources and exchange them over HTTP using a consistent REST API. Resources are the building blocks of FHIR. They represent a variety of healthcare entities, such as patients, encounters, observations, and more. They can be grouped into modules (you will see them on the landing page of the official FHIR spec).

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Data Exchange

As mentioned above, FHIR resources can be exchanged via HTTP in a RESTful manner. This is the most common way to exchange FHIR data. Most HTTP requests are one of these: 
# Read a resource
GET  /fhir/{resourceType}

# Search for resources
GET  /fhir/{resourceType}?name=Doe&gender=male&_count=10

# Read a specific resource
GET  /fhir/{resourceType}/{id}

# Create a resource
POST /fhir/{resourceType}

# Update a resource
PUT  /fhir/{resourceType}/{id}
And most responses are either:

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Try it (2 minutes)

If you have a FHIR server running (TLQ or any other), do these three tiny checks.
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1) Ask the server what it supports

The best “starting page” of any FHIR server is its CapabilityStatement:
curl -H "Accept: application/fhir+json" \
  "http://localhost:8080/fhir/metadata"
Look for:
  • Supported resource types
  • Supported interactions (read, search-type, update, …)
  • Supported search parameters per type
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2) Read one resource

Pick a resource type and ID you know exists and try a read:
curl -H "Accept: application/fhir+json" \
  "http://localhost:8080/fhir/Patient/example"
Two things to notice:
  • resourceType tells you what you’re looking at
  • meta.versionId and meta.lastUpdated tell you about history/versioning
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3) Run your first search

Search returns a Bundle (type searchset):
curl -H "Accept: application/fhir+json" \
  "http://localhost:8080/fhir/Patient?_count=5"
Skim the response for:
  • Bundle.entry[] (the results)
  • Bundle.total (if the server includes it)

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Next

Resources

Understand resourceType, ids, meta, and references

CRUD

Create and update resources safely

Search

Query and page through results

API Reference

Endpoints, headers, and error formats