> For the complete documentation index, see [llms.txt](https://docs.umbraco.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.umbraco.com/umbraco-cms/17.latest/extend-your-project/backoffice-extensions/extending-overview.md).
# Extensions Overview
The backoffice architecture is based on Extensions. Everything in the UI is Extensions which makes almost any parts of the UI extendable. Enabling you to append, replace, or remove parts.
The following screenshot highlights some elements that are extensions. However, a single image cannot fully illustrate this, so we recommend exploring the options in more detail in the [Extension Types](#extension-types) article.
In this section, you can find the common terms, concepts and guides used to extend the Umbraco backoffice.
## [Extension Registry](/umbraco-cms/17.latest/extend-your-project/backoffice-extensions/extending-overview/extension-registry.md)
How to register extensions or manipulate others.
## [Extension Types](/umbraco-cms/17.latest/extend-your-project/backoffice-extensions/extending-overview/extension-types.md)
An overview of the different ways to append functionality.
## [Extension Conditions](/umbraco-cms/17.latest/extend-your-project/backoffice-extensions/extending-overview/extension-conditions.md)
Make your extension appear only when certain conditions are met.
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