# Data Policies

Data policies determine what users see when they query data in a table they have access to.

## How-to guides

* [Author a masking data policy](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/how-to-guides/data-policy-tutorial)
* [Author a minimization policy](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/how-to-guides/minimization-tutorial)
* [Author a purpose-based restriction policy](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/how-to-guides/purpose-tutorial)
* [Author a restricted data policy](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/how-to-guides/restricted-data-policies)
* [Author a row-level policy](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/how-to-guides/row-redaction-tutorial)
* [Author a time-based restriction policy](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/how-to-guides/time-based-tutorial)
* [Policy certifications and diffs](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/how-to-guides/manage-policies-per-data-source): Certify policies and view policy diffs on a data source.

## Reference guides

* [Data policies reference guide](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/reference-guides/data-policies): This guide describes how data policies work in Immuta.
* [Masking policies](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/reference-guides/masking-matrix-functions): This guide describes the types of masking policies available and when to use each.
* [Row-level policies](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/reference-guides/row-redaction-explained): Row-level policies compare data values with user metadata at query-time to determine whether or not the querying user should have access to the individual rows of data.
* [Limit to purpose policies](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/reference-guides/limit-to-purpose-policies): This guide describes how purposes are used in data policies.
* [Custom WHERE clause functions](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/reference-guides/custom-where-clause-functions): This guide describes the custom functions you can use to extend the PostgreSQL WHERE syntax.
* [Lookup tables](https://documentation.immuta.com/latest/governance/author-policies-for-data-access-control/authoring-policies-in-secure/data-policies/reference-guides/lookup-tables): If user metadata is stored in a table in the same data platform where a policy is enforced, it is not necessary to move that user metadata in Immuta. This guide describes how to reference the user metadata in those tables directly using custom WHERE functions in data policies.


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