The Serialization API is new in Drupal 8. It is largely based on the Symfony Serializer component, so their documentation is also relevant.
The Serialization API depends on Symfony's Serializer component.
Core supports JSON and XML, as well as HAL-JSON. It is easy to add support for other formats.
Core supports serialization for content entities, their fields, and field items. It is easy to add support for other classes, and also to