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When used as a declaration modifier, the new keyword explicitly hides a member that is inherited from a base class. When you hide an inherited member, the derived version of the member replaces the base class version. This assumes that the base class version of the member is visible, as it would already be hidden if it were marked as private or, in some cases, internal . Although you can hide public or protected members without using the new modifier, you get a compiler warning. If you use new to explicitly hide a member, it suppresses this warning.

You can also use the new keyword to create an instance of a type or as a generic type constraint .

To hide an inherited member, declare it in the derived class by using the same member name, and modify it with the new keyword. For example:

public class BaseC
    public int x;
    public void Invoke() { }
public class DerivedC : BaseC
    new public void Invoke() { }
In this example, BaseC.Invoke is hidden by DerivedC.Invoke. The field x is not affected because it is not hidden by a similar name.
Name hiding through inheritance takes one of the following forms:
Generally, a constant, field, property, or type that is introduced in a class or struct hides all base class members that share its name. There are special cases. For example, if you declare a new field with name N to have a type that is not invocable, and a base type declares N to be a method, the new field does not hide the base declaration in invocation syntax. For more information, see the Member lookup section of the C# language specification.
A method introduced in a class or struct hides properties, fields, and types that share that name in the base class. It also hides all base class methods that have the same signature.
An indexer introduced in a class or struct hides all base class indexers that have the same signature.
It is an error to use both new and override on the same member, because the two modifiers have mutually exclusive meanings. The new modifier creates a new member with the same name and causes the original member to become hidden. The override modifier extends the implementation for an inherited member.
Using the new modifier in a declaration that does not hide an inherited member generates a warning.
Examples
In this example, a base class, BaseC, and a derived class, DerivedC, use the same field name x, which hides the value of the inherited field. The example demonstrates the use of the new modifier. It also demonstrates how to access the hidden members of the base class by using their fully qualified names.
public class BaseC
    public static int x = 55;
    public static int y = 22;
public class DerivedC : BaseC
    // Hide field 'x'.
    new public static int x = 100;
    static void Main()
        // Display the new value of x:
        Console.WriteLine(x);
        // Display the hidden value of x:
        Console.WriteLine(BaseC.x);
        // Display the unhidden member y:
        Console.WriteLine(y);
Output:
In this example, a nested class hides a class that has the same name in the base class. The example demonstrates how to use the new modifier to eliminate the warning message and how to access the hidden class members by using their fully qualified names.
public class BaseC
    public class NestedC
        public int x = 200;
        public int y;
public class DerivedC : BaseC
    // Nested type hiding the base type members.
    new public class NestedC
        public int x = 100;
        public int y;
        public int z;
    static void Main()
        // Creating an object from the overlapping class:
        NestedC c1  = new NestedC();
        // Creating an object from the hidden class:
        BaseC.NestedC c2 = new BaseC.NestedC();
        Console.WriteLine(c1.x);
        Console.WriteLine(c2.x);
Output:
If you remove the new modifier, the program will still compile and run, but you will get the following warning:
The keyword new is required on 'MyDerivedC.x' because it hides inherited member 'MyBaseC.x'.
C# language specification
For more information, see The new modifier section of the C# language specification.
See also
C# Reference
C# Programming Guide
C# Keywords
Modifiers
Versioning with the Override and New Keywords
Knowing When to Use Override and New Keywords