The following rules outline the naming guidelines for interfaces:

• Name interfaces with nouns or noun phrases, or adjectives that describe behavior. For example, the interface name IComponent uses a descriptive noun. The interface name ICustomAttributeProvider uses a noun phrase. The name IPersistable uses an adjective.
• Use Pascal case.
• Use abbreviations sparingly.
• Prefix interface names with the letter I, to indicate that the type is an interface.
• Use similar names when you define a class/interface pair where the class is a standard implementation of the interface. The names should differ only by the letter I prefix on the interface name.
• Do not use the underscore character (_).

The following are examples of correctly named interfaces.

Public Interface IServiceProvider
Public Interface IFormatable
[C#]
public interface IServiceProvider
public interface IFormatable

The following code example illustrates how to define the interface IComponent and its standard implementation, the class Component.

Public Interface IComponent
   ' Implementation code goes here.
End Interface

Public Class Component
   Implements IComponent
   ' Implementation code goes here.
End Class

[C#]
public interface IComponent 
{
   // Implementation code goes here.
}
public class Component: IComponent 
{
   // Implementation code goes here.
}

See Also

Design Guidelines for Class Library Developers | Base Class Usage Guidelines