What is the difference between List and IList in C#?

The main difference between List and IList in C# is that List is a class that represents a list of objects which can be accessed by index while IList is an interface that represents a collection of objects which can be accessed by index. The IList interface implemented from two interfaces and they are ICollection and IEnumerable.

List and IList are used to denote a set of objects. They can store objects of integers, strings, etc. There are methods to insert, remove elements, search and sort elements of a List or IList. The major difference between List and IList is that List is a concrete class and IList is an interface. Overall, List is a concrete type that implements the IList interface.

Example 1

using System;
using System.Collections.Generic;
namespace DemoApplication{
   class Demo{
      static void Main(string[] args){
         IList<string> ilist = new IList<string>();
         //This will throw error as we cannot create instance for an IList as it is an interface.
         ilist.Add("Mark");
         ilist.Add("John");
         foreach (string list in ilist){
            Console.WriteLine(list);
         }
      }
   }
}

Example 2

 Live Demo

using System;
using System.Collections.Generic;
namespace DemoApplication{
   class Demo{
      static void Main(string[] args){
         IList<string> ilist = new List<string>();
         ilist.Add("Mark");
         ilist.Add("John");
         List<string> list = new List<string>();
         ilist.Add("Mark");
         ilist.Add("John");
         foreach (string lst in ilist){
            Console.WriteLine(lst);
         }
         foreach (string lst in list){
            Console.WriteLine(lst);
         }
         Console.ReadLine();
      }
   }
}

Output

The output of the above code is

Mark
John
Mark
John