As an American, I am burdened by two co-existing spellings of the object of my affection — place and practice. Theatre or Theater? Research tells me that the “er” version was introduced by Noah Webster in the 1830s as part of his attempt to Americanize spellings of English words. We lost “colour” and all those other extra “u”s, and we gained this new spelling of “theatre” as “theater”.
Well. I like “theatre” as do many of my theatre-writing colleagues. I shall use the word spelled as theater when I am directly quoting someone else who spells it that way in print or when I’m referencing the name of a building or producing company that has chosen to spell its name that way. Otherwise, Webster be damned, this American gal is going with theatre.