In this talk, we will discuss - independently of my previous talk on Feb. 9 - how depth two (D2) algebra extensions are Galois with coacting quantum groupoids. We will discuss the correspondence of type of Hopf algebroid with type of D2 ring extension. Time permitting, we will discuss how depth two is a notion of normal subring, and what D3 or DN might be in a more extensive Galois theory for noncommutative rings.