# Defining Interfaces

Define an interface with the interface keyword, a name starting with I, and members with no bodies. A class implements it by listing it after the colon, after its base class, and writing every member as public.

![Cheat sheet: Defining Interfaces](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/11/959b3cdd37004347aeaf91494bacc5b9.webp)

- Category: C#
- Level: Journeyman
- Tags: c-sharp, Implementing an Interface, Interface (c-sharp), OOP
- Updated: November 3, 2026

Source: https://www.ask-codey.com/cheat-sheets/interfaces-in-csharp-defining-interfaces-cheat-sheet