How ripe (or green) does a tomato have to be to save seeds?

I have some tomato's I wished I had saved seeds from but do have some green ones left. Does anyone know if I can still save the seeds or does the fruit have to reach a certain level of maturity?

Thanks-

Has to reach maturity. Let some ripen in the window if nothing else and them then they are good to go. Green tomatoes aren't completely mature.

That should work. What kind did you have?

This one is a White Tomesol. It was a real show stopper this year and very confusing but tasty tomato for all the friends I gave them too. I just ate and gifted too many and spaced the seeds-

So I am guessing it is better to even let them ripen past the stage of being edible for the sake of keeping the seed rather than on the green side?

Yes, Thats pretty much the way to do it.