Do I have to install Crown Molding before or after installing Styrofoam ceiling tiles?

You can actually do it both ways.  So, if you have a Crown Molding installed already or want to install it before the tiles, here is what you should know: 1. It will take you about the same time to install the full tiles as it will take you to measure and cut to fit the perimeter tiles if you install the crown molding before the tiles.  2. You do not need to caulk the top of the crown molding until you install the tiles. If you decide to go the other route and install the crown molding after you should consider this: 1. It is much faster to cut the perimeter tiles if you do not have to measure them exactly as it is in the case of installing the Crown Molding before.  2. Depending on the design of your tiles, large gaps may be created after you install the Crown molding over the tiles.  This will mean that caulking will take you longer and you may have to re-caulk as caulk does shrink.