It’s no secret I love the AP Stylebook. It always reminds me of exactly what I’d forgotten and is my go to resource when I can’t remember a grammar rule. I got this update emailed to me yesterday afternoon. I can’t summarize it any better than they did:
“ensure, insure, assure
Use ensure to mean guarantee: Steps were taken to ensure accuracy.
Use insure for references to insurance: The policy insures his life.
Use assure to mean to make sure or give confidence: She assured us the statement was accurate.”
There it is, in simple terms the difference between ensure, insure and assure.