What interfaces do all arrays implement in C#?

From the documentation (emphasis mine):

[...] the Array class implements the System.Collections.Generic.IList<T>, System.Collections.Generic.ICollection<T>, and System.Collections.Generic.IEnumerable<T> generic interfaces. The implementations are provided to arrays at run time, and therefore are not visible to the documentation build tools.

EDIT: as Jb Evain points out in his comment, only vectors (one-dimensional arrays) implement the generic interfaces. As to why multi-dimensional arrays don't implement the generic interfaces, I'm not quite sure since they do implement the non-generic counterparts (see the class declaration below).

The System.Array class (i.e. every array) also implements these non-generic interfaces:

public abstract class Array : ICloneable, IList, ICollection, IEnumerable, IStructuralComparable, IStructuralEquatable

You can find the answer to your question empirically using a small code snippet:

foreach (var type in (new int[0]).GetType().GetInterfaces())
    Console.WriteLine(type);

Running the above snippet would result in the following output (on .NET 4.0):

System.ICloneable
System.Collections.IList
System.Collections.ICollection
System.Collections.IEnumerable
System.Collections.IStructuralComparable
System.Collections.IStructuralEquatable
System.Collections.Generic.IList`1[System.Int32]
System.Collections.Generic.ICollection`1[System.Int32]
System.Collections.Generic.IEnumerable`1[System.Int32]

(`1 means <T>)

After .NET 4.5 (.NET Standard 1.0 and later), there's two additional interfaces:

System.Collections.Generic.IReadOnlyList`1[System.Int32]
System.Collections.Generic.IReadOnlyCollection`1[System.Int32]

Starting with .NET 4.5, arrays also implement the interfaces System.Collections.Generic.IReadOnlyList<T> and System.Collections.Generic.IReadOnlyCollection<T>.

Thus, when using .NET 4.5, the complete list of interfaces implemented by arrays becomes (obtained using the method presented in Hosam Aly's answer):

System.Collections.IList
System.Collections.ICollection
System.Collections.IEnumerable
System.Collections.IStructuralComparable
System.Collections.IStructuralEquatable
System.Collections.Generic.IList`1[System.Int32]
System.Collections.Generic.ICollection`1[System.Int32]
System.Collections.Generic.IEnumerable`1[System.Int32]
System.Collections.Generic.IReadOnlyList`1[System.Int32]
System.Collections.Generic.IReadOnlyCollection`1[System.Int32]

Strangely, it seems that it was forgotten to update the documentation on MSDN to mention these two interfaces.

Carefully on array interfaces, they may implement them but actually they don't really do this... Take a loon on the following code:

            var x = new int[] { 1, 2, 3, 4, 5 };
        var y = x as IList<int>;
        Console.WriteLine("The IList:" + string.Join(",", y));
        try
        {
            y.RemoveAt(1);
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }
        Console.WriteLine(string.Join(",", y));

It produces the following output: result

So parsing works but not everything is supported which is correct from fixed length collection perspective but quite wrong if you really believe that it is a list. There goes Liskov principle from SOLID :(.

For testing fast this will help.