An earthquake or sharp impact can dislodge a heavy bookshelf hanging from drywall. Books weigh about 12 ounces each on average, and some hardcover books can weigh over a pound. The heavy weight means that when you hang a bookshelf from the wall, it has to be securely attached, which in turn means you should avoid wall anchors. The strongest anchors -- toggle bolts -- can hold 50 pounds or more, but they anchor against the drywall, which may crack under that much weight. Hanging the shelves from the wall studs is a safer alternative, and you can do it by using a French cleat instead of unsightly metal corner brackets.