Duplicating Layers

If you have a picture of Elvis, and you want to make Elvis twins, just drag the name of the layer onto the New-Layer icon at the bottom of the Layers palette. This icon has two purposes: It will duplicate a layer if you drag one on top of it, or it will create a new empty layer if you just click it. You can also hold Option (Mac) or Alt (Windows) when dragging a layer up or down within the layers stack, or type Command-J (Mac) or Ctrl-J (Windows) to duplicate the currently active layer. Just make sure you don't have a selection active; otherwise, this command will copy only the area that is selected instead of the whole layer.