Difference between IEnumerable and IEnumerable?

Question

What is the difference between IEnumerable and IEnumerable?

I\'ve seen many framework classes implementing both these interfaces,

Answer 1

As to why you see classes defining both, enough though IEnumerable< T > implements IEnumerable, its not needed but is is nice in a self documenting to list the sub interfaces at times. Consider

interface IA { }
interface IB : IA { }

class A : IB {} // legal, IB implements IA

class B : IA, IB {} // also legal, possible more clear on intent