> For the complete documentation index, see [llms.txt](https://docs.stackai.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.stackai.com/technical-reference/workflow-execution.md).

# Workflow Execution

Understand how data moves through a workflow, how nested runs behave, and what happens when execution fails or pauses.

* [Execution Order and Node Dependencies](/technical-reference/workflow-execution/execution-order-and-node-dependencies.md)
* [Inputs, Outputs, and Variable References](/technical-reference/workflow-execution/inputs-outputs-and-variable-references.md)
* [Data Types, Lists, Missing Values, and Empty Results](/technical-reference/workflow-execution/data-types-lists-missing-values-and-empty-results.md)
* [Branches, Conditions, and Routing](/technical-reference/workflow-execution/branches-conditions-and-routing.md)
* [Loops: Item Mapping, Concurrency, and Result Order](/technical-reference/workflow-execution/loops-item-mapping-concurrency-and-result-order.md)
* [Loop Failures and Partial Results](/technical-reference/workflow-execution/loop-failures-and-partial-results.md)
* [StackAI Project and Beta Nodes](/technical-reference/workflow-execution/stackai-project-and-beta-nodes.md)
* [Nested Workflow Inputs, Outputs, and Identity](/technical-reference/workflow-execution/nested-workflow-inputs-outputs-and-identity.md)
* [Nested Workflow Version and Environment Selection](/technical-reference/workflow-execution/nested-workflow-version-and-environment-selection.md)
* [Timeouts and Execution Limits](/technical-reference/workflow-execution/timeouts-and-execution-limits.md)
* [Retries, Fallbacks, and Error Branches](/technical-reference/workflow-execution/retries-fallbacks-and-error-branches.md)
* [External Side Effects and Safe Retries](/technical-reference/workflow-execution/external-side-effects-and-safe-retries.md)
* [Paused Runs, Human Input, and Resumption](/technical-reference/workflow-execution/paused-runs-human-input-and-resumption.md)
* [Cancellation and Run Status](/technical-reference/workflow-execution/cancellation-and-run-status.md)
* [Batch Execution and Per-Item Results](/technical-reference/workflow-execution/batch-execution-and-per-item-results.md)


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