# Project Structure Introduction to project structure and components. [//]: # (TODO: split into parts accordingly to the table of contents) This topic considers the concept of projects based on the IntelliJ Platform and related subjects, such as _modules_, _facets_, _libraries_, and _SDK_. The project structure and Java classes available to manage projects and modules are discussed. > Internal changes related to a significant redesign of the representation of project models are included in 2020.3 release; please see [blog post](https://blog.jetbrains.com/platform/2020/10/new-implementation-of-project-model-interfaces-in-2020-3/) for details. > This shouldn't affect any plugins using the IntelliJ API properly and which don't access internal classes. > {style="note"} ## Project and Its Components This section briefly discusses the IDEA project structure, project components, and related terms. For more information about projects and their components, refer to [Project](https://www.jetbrains.com/help/idea/about-projects.html), [Module](https://www.jetbrains.com/help/idea/creating-and-managing-modules.html), [Library](https://www.jetbrains.com/help/idea/working-with-libraries.html), [Facet](https://www.jetbrains.com/help/idea/adding-support-for-frameworks-and-technologies.html#facets) in the IntelliJ IDEA Web Help. Use [`ProjectSettingsService`](%gh-ic%/platform/lang-impl/src/com/intellij/openapi/roots/ui/configuration/ProjectSettingsService.java) to open related entries in Project Structure dialog. ### Project In the IntelliJ Platform, a _project_ encapsulates all of a project's source code, libraries, and build instructions into a single organizational unit. Everything done using the IntelliJ Platform SDK is done within the context of a project. A project defines collections referred to as _modules_ and _libraries_. Depending on the project's logical and functional requirements, you can create a _single-module_ or a _multi-module_ project. ### Module A _module_ is a discrete unit of functionality that can be run, tested, and debugged independently. Modules include such things as source code, build scripts, unit tests, deployment descriptors, etc. In a project, each module can use a specific SDK or inherit the SDK defined at the project level (see the [SDK](#sdk) section below in this document). A module can depend on other modules of the project. ### Library A _library_ is an archive of compiled code (such as JAR files) on which modules depend. The IntelliJ Platform supports three types of libraries: * **Module Library**: the library classes are visible only in this module, and the library information is recorded in the module's .iml file. * **Project Library**: the library classes are visible within the project, and the library information is recorded in the project's .ipr file or in .idea/libraries. * **Global Library**: the library information is recorded in the applicationLibraries.xml file in the ~/.IntelliJIdea/config/options directory. Global libraries are similar to project libraries but are visible for different projects. For more information about libraries, refer to [Library](https://www.jetbrains.com/help/idea/working-with-libraries.html). ### SDK Every project uses a Software Development Kit (_SDK_). For Java projects, SDK is referred to as JDK (Java Development Kit). The SDK determines which API library is used to build the project. If a project is multi-module, the project SDK is common for all modules within the project by default. Optionally, a project can configure an individual SDK for each module. For more information about SDKs, see [Working with SDKs](https://www.jetbrains.com/help/idea/working-with-sdks.html) in the IntelliJ IDEA Web Help. ### Facet A _facet_ represents a certain configuration, specific for a particular framework/technology associated with a module. A module can have multiple facets. E.g., Spring-specific configuration is stored in a Spring facet. Facets are documented under [Facet](https://www.jetbrains.com/help/idea/adding-support-for-frameworks-and-technologies.html#facets) and [Language and Framework Specific Guidelines](https://www.jetbrains.com/help/idea/language-and-framework-specific-guidelines.html) in the IntelliJ IDEA Web Help. ## Additional Information For more information on each of these entities, see: - [Project](project.md) - [Module](module.md) - [SDK](sdk.md) - [Library](library.md) - [External system integration](external_system_integration.md) (for projects imported from Gradle or similar build systems)