Is it possible to teach without a degree in the field your want to teach?

I think that teaching classes would be interesting. I have a lot of industry experience, but I never actually got a degree in the field I work in, and I don't have any sort of degree that deals with teaching. Is it possible to get a job as a teacher without those?

Edit: I'm in the US specifically looking at teaching college courses, but K-12 could be interesting, too.