> For the complete documentation index, see [llms.txt](https://developer.harness.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.harness.io/release-orchestration/3.0/execution/activity-execution-flow.md).

# Activity Execution Flow

Activities execute based on their dependencies and type.

### Activity Execution <a href="#activity-execution" id="activity-execution"></a>

#### Pipeline Activities <a href="#pipeline-activities" id="pipeline-activities"></a>

Pipeline activities (automated activities) execute by:

* Triggering the associated Harness pipeline
* Passing activity inputs to the pipeline
* Tracking pipeline execution status
* Capturing pipeline outputs

#### Manual Activities <a href="#manual-activities" id="manual-activities"></a>

Manual activities execute by:

* Going into an "on hold" or "waiting for input" state
* Sending notifications to assigned users
* Waiting for users to record their inputs and finalize them
* Completing once user provides sign-off or input

#### Subprocess Activities <a href="#subprocess-activities" id="subprocess-activities"></a>

Subprocess activities execute by:

* Invoking the nested process
* Executing the subprocess phases and activities
* Propagating status back to the parent process

### Dependencies <a href="#dependencies" id="dependencies"></a>

Activities execute based on their dependencies:

* Activities wait for their dependencies to complete
* Dependencies can be configured between activities within a phase
* Dependencies control the execution order

### Related Topics <a href="#related-topics" id="related-topics"></a>

* [Executing a release](/release-orchestration/use-release-orchestration/release-orchestration-execution/executing-a-release.md)
* [Parallel vs Sequential Execution](/release-orchestration/3.0/handle-failures/parallel-vs-sequential-execution.md)
* [Error handling](/release-orchestration/use-release-orchestration/release-orchestration-execution/error-handling.md)