[fjtorres]

Romance is first and foremost about the relationship between two people. The story can be wrapped in any plot, theme, and environment but if the story falls apart without the relationship it is a ROMANCE. It takes two to tango.

A lot like SF, where if you take out the Scientific (or speculative science) element the story falls apart.

You can have a romance in any genre but the story has to be *about* the romance to fit the genre. Beyond that you'll likely find disagreement over the particulars. Does it need a Happily Ever After or will a Happily for now suffice? Does the relationship have to be consumated or even acknowledged? Does it have to be heterosexual or even among the living?

Very broad field.
In fact, as DG points out in his charts, a good portion of romance gets miscategorized as general fiction or litfic. Just as with SF, there are naysayers who insist that if it's really really good it can't be romance (or SF). Right now, one of the most popular writers of romance (tearjerker specialist Nicholas Sparks) insists he doesn't write romance. Except his stories are all about romantic relationships and nothing but. Walks like a duck, quacks like a duck? It's a duck.