This document provides an overview of interfaces and namespaces in C#. It defines interfaces as a syntactic contract that classes inherit from to define common properties, methods, and events, while classes implement the specific functionality. Namespaces are used to avoid naming conflicts by logically grouping classes. Namespaces can be defined using the namespace keyword and items within a namespace can be accessed by prepending the namespace name or using the using keyword to import namespace names. Nested namespaces can also be defined.