When a Namespace is declared inside the other namespace that declaration is called nesting namespaces. You can nest namespaces to any level you want. There are 2 ways to nest the namespaces which are as under:
- We have nested namespaces to 3 levels. The fully qualified name of Customer class in the below code snippet is ABC.XYZ.PQR.Customer
using System;namespace ABC 
{ 
    namespace XYZ 
    { 
        namespace PQR 
        { 
            //Our Types(Classes,Interfaces,Structures,Delegates,Enumerations etc..) 
            class Customer 
            { 
                //Class code 
            } 
        } 
    } 
} 
- Another approach to nest namespaces is using the dot operator.
using
 System;
namespace ABC.XYZ.PQR //Nesting namespaces using dot operator 
{ 
    // Types(Classes,Interfaces,Structures,Delegates,Enumerations etc..)