Introduction to Composer
We use Composer to manage Magento components and their dependencies. Using Composer to get the Magento software metapackage provides the following advantages:
- Reuse third-party libraries without bundling them with source code
 - Reduce extension conflicts and compatibility issues by using a component-based architecture with robust dependency management
 - Adhere to PHP-Framework Interoperability Group (FIG) standards
 - Repackage Magento Open Source with other components
 - Use the Magento software in a production environment
 
You must create a Composer project from our metapackage if you want to use the Magento Web Setup Wizard to upgrade the Magento software and third-party extensions.
Links to Magento code
The key to developing any Magento component is its composer.json, which specifies version and dependency information for a component, among other things. You can look at Magento 2 code, such as:
- Metapackage, look at 
<magento_root>/composer.json. - Customer module
 - Luma theme
 - en_us language package
 
For more information
For more information about Composer, see the Composer documentation.