Theater is the verb, theatre is the noun

My understanding is:

TheatER = the place where a show is held

TheatRE = the art of acting, etc.

I was curious so I actually looked this up...Theatre and Theater are both nouns that can be used interchangeably according to Websters. So use whichever spelling you prefer because they mean exactly the same thing.

I explain it Dan's way, except that the word "centre" is often used by real estate developers to give their organizations or product snob appeal. The names of arts buildings, especially those named for wealthy patrons, are often "theatres." To me, and may be JUST me, using the british spellings of anything reads as pretentious. It's just so wannabe. In use the words seem interchangeable, but choosing one versus the other does have a different connotation to different audience targets. For those reasons, and because I sense that a lot - not all - of people will spell it "theatre" to elevate their status, I actively fight to use "theatre" in any context. (I am an arts marketer, only 10% of what I do has anything to do with theater.)

Thanks to all of you (except Melanie) who answered my question. My newly formed group was split on whether to use theater/re. We finally decided on theater.