Crown moulding is a decorative element that is installed where the wall meets the ceiling. Molding typically comes in wood or plaster, but you can find it in other materials such as polyurethane as well. You've probably seen baseboard molding or molding around doors and windows, but crown molding adds something extra to a room.  No matter the style you use or where you use it, crown molding transforms a room. It makes a space more grown-up, classy or opulent. Crown molding is used mostly for decoration today. In the past, crown molding served to cover cracks between the wall and the ceiling.