Subscribers in multiple mailing lists?

I have a mailing list that gets subscribers from a newsletter form (fine - no problem). 

But I want to set up a second mailing list and I want some of my existing subscribers to also be on that mailing list. 

Is it possible for a subscriber to be on TWO mailing lists simultaneously? Or can this ONLY be managed via tags?

I would like to know the answer to this as well.