Good Books on BDSM

I was wondering if any of you had suggestions for good books that deal with BDSM. I’m talking about books that deal with the relationship aspect, and not necessarily erotica (although, do any of you think I’d honestly pass on erotica?). A book that sets up guidelines, would be great too. The books can be from the perspective of any of the possible players in a BDSM relationship. Thanks in advance ;)!