# 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](https://docs.finngen.fi/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)
* [Exclude and Remove codes from Concept Set](https://docs.finngen.fi/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)
* [Simplify Concept Sets that use standard code descendants](https://docs.finngen.fi/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)
* [Create Concept Sets using equivalent standard and non-standard codes](https://docs.finngen.fi/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)
* [View standard code hierarchy in Atlas](https://docs.finngen.fi/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)