Crown moulding is an affordable way to upgrade any room in your home by adding a feeling of warmth and elegance. Without crown moulding, even the most beautifully decorated room looks unfinished. By definition, crown moulding runs along the top of a wall where it meets the ceiling. Wider moulding tends to have a more stately effect. But because ceilings and walls are rarely perfectly square, crown moulding can be tricky to install. That's why most "do-it-yourself" homeowners will hire a professional when it comes to installing crown.