# Introduction
This is the openEO Developer Documentation for API versions 0.4.x.
The openEO API defines a HTTP API that lets cloud back-ends with large Earth observation datasets communicate with front end analysis applications in an interoperable way.
As an overview, the openEO API specifies how to
- discover which Earth observation data and processes are available at cloud back-ends,
- execute (chained) processes on back-ends,
- run user-defined functions (UDFs) on back-ends where UDFs can be exposed to the data in different ways,
- download (intermediate) results, and
- manage user content including billing.
The API is defined as an OpenAPI 3.0 (opens new window) JSON file.