# Annotation Groups
An annotation group is the category that encompasses all of the classes in your project. It answers the question: **"What types of things are labeled in this dataset?"**
Every project has an annotation group. Projects that share the same annotation group also share their class list and annotations, making it possible to reuse labeled data across multiple projects without duplicating images.
### Why Annotation Groups Matter
The same image can be annotated in different ways depending on what you are trying to detect. For example, an image of a chess board could be labeled with:
* **Chess pieces** (pawn, knight, bishop, rook, queen, king) in one project
* **Board games** (chess, checkers, backgammon) in another project
These two projects have different annotation groups because they describe different categories of things. Each project maintains its own set of annotations for the shared image, and the image is only counted once toward your usage.
When multiple projects share the same annotation group, any annotation changes made in one project are reflected in the others. This is useful when you want to build specialized datasets from a common pool of labeled images.
### Setting Up Shared Annotations
When creating a project, you can choose to share annotations with other projects:
1. Check **"Share image annotations with other projects"** during project creation.
2. In the annotation group field, either select an existing annotation group from the autocomplete suggestions or type a new name to create one.
3. Any images added to this project that also exist in other projects with the same annotation group will share their annotations.
If you do not enable shared annotations, the project is assigned a unique annotation group automatically. You can change a project's annotation group later from the project settings.
{% hint style="warning" %}
When you share annotations across projects, editing or deleting an annotation in one project affects all other projects in the same annotation group. Make sure your team is aware of this before enabling shared annotations.
{% endhint %}
### Identifying Shared Annotations
Look for the chain-link icon 🔗 on images or projects to identify shared annotations
* The **annotation tool**, next to the image
* The **asset library**, on image previews
* **projects** which share the same annotation group on another show up with it on project list
Project listing showing shared annotation group icon and tooltip
Annotation Tool showing the shared icon and tooltip
Hovering over the chain-link icon shows a tooltip listing the other projects that share the image. This helps you understand the impact of annotation changes before making them.
