I found a 8" hole that goes underneath my foundation. Should I be concerned? Will this hole undermine the foundation? How should I go about fixing it?
Thanks.

What kind of foundation and where does the hole lead to?

I have seen homes (on piles) in Louisiana after Katrina that were still sound even when the boy in the family could crawl under the slab to intall cable.

Other homes on thick slabs can survive well.

If you are really concerned, hire a professional engineer(definitely not a contractor that does work) to look at the situation. The engineer is working for you and should not be a contractor, but he can make a report or give you a design for correction if it is needed.

The hole goes from the outside into a crawlspace. It's a poured concrete type foundation. There are no piles or slab.
Thanks.