1. Classes: Classes are the building blocks of C# programming. They provide a way to define a type of object that can store data, provide methods for manipulating that data, and serve as a template for creating objects of the same type.

2. Inheritance: Inheritance is a way of creating a new class from an existing one. This allows a class to inherit the properties and methods of the base class, and also allows for specialization of the new class.

3. Interfaces: Interfaces are a way of defining a contract between a class and its users. It defines the methods and properties that a class must implement, allowing for code reuse and better separation of concerns.

4. Generics: Generics enable you to write code that can work with any type, rather than being restricted to a specific type. This allows for greater flexibility and code reuse.

5. Delegates and Events: Delegates and events allow for the creation of callbacks that can be used to notify code of certain events. This allows for more loosely coupled code, and makes it easier to write code that is extensible.

6. LINQ: LINQ (Language Integrated Query) is a set of language features that allow for querying data in a concise and type-safe manner. This allows for more efficient data manipulation and makes it easier to work with data sources.