> For the complete documentation index, see [llms.txt](https://docs.finngen.fi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.finngen.fi/working-in-the-sandbox/which-tools-are-available/atlas/detailed-guide/how-to-define-a-cohort-in-atlas/concept-sets.md).

# Concept Sets

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In Atlas, the cohort definition starts by creating a **Concept Set** using medical codes. The Concept Set is then used to create cohorts using additional criteria defined in **Cohort Definitions**.
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This section contains advanced Concept Set creation tutorials.

### Topics in the section

* [Create Concept Sets using standard code descendants](/working-in-the-sandbox/which-tools-are-available/atlas/detailed-guide/how-to-define-a-cohort-in-atlas/concept-sets/selecting-descendants-for-a-concept-set-in-atlas.md)
* [Exclude and Remove codes from Concept Set](/working-in-the-sandbox/which-tools-are-available/atlas/detailed-guide/how-to-define-a-cohort-in-atlas/concept-sets/exclude-and-remove-codes-from-concept-set.md)
* [Simplify Concept Sets that use standard code descendants](/working-in-the-sandbox/which-tools-are-available/atlas/detailed-guide/how-to-define-a-cohort-in-atlas/concept-sets/simplify-concept-sets-that-use-standard-code-descendants.md)
* [Create Concept Sets using equivalent standard and non-standard codes](/working-in-the-sandbox/which-tools-are-available/atlas/detailed-guide/how-to-define-a-cohort-in-atlas/concept-sets/find-mapped-equivalents-for-standard-and-non-standard-codes-in-atlas.md)
* [View standard code hierarchy in Atlas](/working-in-the-sandbox/which-tools-are-available/atlas/detailed-guide/how-to-define-a-cohort-in-atlas/concept-sets/viewing-the-hierarchy-of-standard-snomed-codes-in-atlas.md)