Difference between IEnumerable and IEnumerable?

What is the difference between IEnumerable and IEnumerable?

I've seen many framework classes implementing both these interfaces, therefore I would like to know what advantages one get by implementing both?

Please have a look how they've been defined:

public interface IEnumerable
{
    [DispId(-4)]
    IEnumerator GetEnumerator();
}
public interface IEnumerable<T> : IEnumerable
{
    IEnumerator<T> GetEnumerator();
}

As we see, IEnumerable derives from IEnumerable, that means whatever IEnumerable has, IEnumerable inherits, then why do we implement both instead of just IEnumerable? Is implementing IEnumerable not enough?

Likewise, there are other similar pairs:

• IList and IList
• ICollection and ICollection

I would like to know about these as well.