## Adding ID lists

### What is an ID list?

An ID List enables you to define a reusable audience segment using user identifiers like `userID`, `stableID`, or `organizationID`.

You can manage ID Lists by manually adding or removing IDs, uploading CSVs, or replacing the entire list.

### Creating an ID list segment

1. Navigate to the **Segments** section in the [Statsig Console](https://console.statsig.com).
2. Click **Create New Segment**.
3. Toggle the segment type from **Conditional** to **ID List**.
   {% figure %}
   ![Create New Segment](/images/segments/add-id-list/af7c5cb3-adc2-4e88-a411-b5844a541e49.png)
   {% /figure %}
4. Select the **ID type** you want to build from.
   {% figure %}
   ![Create New Segment](/images/segments/add-id-list/958b7545-7f23-4559-8a66-99af01d39952.png)
   {% /figure %}

### Managing IDs

Once inside your ID List segment, you have a variety of options:

* **Manual Entry**: Enter IDs directly into the input box.
  {% figure %}
  ![Create New Segment](/images/segments/add-id-list/ee94e6bc-475b-47a0-96a7-5ddba398d58c.png)
  {% /figure %}
* **Upload CSV**: Import a list of IDs from a CSV.
* **Bulk Actions**: Choose how your input affects the existing list:
  * **Add**: Add IDs to the list
  * **Remove**: Remove matching IDs from the list
  * **Replace**: Clear all IDs and replace with a new list

You can also sync an ID list segment from sources such as [Amplitude Cohorts](https://help.amplitude.com/hc/en-us/articles/4789303290011), [Segment Audiences](/integrations/data-connectors/segment#syncing-statsig-segment-id-lists-with-segment-personas-audiences), or a custom source using the [Console API](/console-api/introduction).

There's a hard limit of 10 million IDs across all ID Lists in your project.

### Keep ID lists small

ID Lists with fewer than 1,000 IDs are synchronized in the same process as feature gates, experiments, and conditional segments, providing high consistency and reliability. ID Lists over 1,000 IDs use a separate synchronization process for scalability, which means they aren't included in the main initialization path (for server SDKs or the local evaluation version of client SDKs) and change propagation takes longer.

Keep each ID List to no more than 1,000 IDs unless the longer propagation time is acceptable.

### Large ID lists

To target hundreds of thousands or millions of users, the more performant approach is to set an attribute on the User object passed to the Statsig SDK. For example, pass `user_type:Paid` or `user_type:Trial` in the User object instead of maintaining large ID Lists. This requires your app to have this information available when calling the Statsig SDK. If your use case requires ID lists larger than 10,000 IDs, contact the Statsig team through Slack.

{% callout type="info" %}
Large ID Lists is currently in limited beta. Contact Statsig Support to enable. Note this is not available for Free/Pro users at this time.
{% /callout %}