The only explanation I have ever heard- abroad or here in Israel- is that the breaking glass is in memory of the destruction of the Temple, as Chocolate Pi explains. Attending my sister-in-law's second marriage, the only glasses around were Duralex, which is hard to break, so I suggested to the rabbi that we wrap up a light bulb. He was shocked and said it wouldn't be a real wedding- so Chocolate Pi, I'm sorry to have to tell you....:-) PS my new brother-in-law, (at 68 yrs old) broke the Duralex glass first stomp. The couple is very happy thank you. Jack The Lad