# Interfaces Guillotina uses interfaces to abstract and define various things including content. Interfaces are useful when defining API contracts, using inheritance, defining schema/behaviors and being able to define which content your services are used for. In the services example, you'll notice the use of `context=IContainer` for the service decorator configuration. In that case, it is used to tell Guillotina that the service is only defined for a container object. Read the [zope.interface documentation](https://zopeinterface.readthedocs.io/en/latest/) for more details about the power of designing around around interfaces and to learn more about how to use it.