Depends where you are going. If you're going to some huge, professional performance in a big city, then you want to dress nicer than you would if you were going to some small production in your Midwestern hometown. (not that you have a Midwestern hometown, just for ex.) In either case, you want to dress nicer than you usually would (no sneakers, no jeans, no loose tees, $5 tank tops, etc.), but this is not compulsory. Plenty of people go to the theater dressed in ordinary clothes. But its generally considered nice to wear nice clothing. But don't go to overboard. It's not the opera. No ballgowns.

So, I would say a cocktail dress or a l. b. d. would be fine, but you would be just as well off in slacks. And there will probably be more women in slacks or a dressy skirt than in a dress.

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