Adobe Illustrator CS

A layer clipping mask is very similar to a clipping mask, with one main difference: instead of masking another selected object or group of objects, it masks entire layers. In reality, layer clipping masks are far easier to control and work with because you aren’t constantly selecting and deselecting objects to define what is or what isn’t in a particular mask. Instead, you use the Layers palette, which you use to organize your artwork anyway, to create these kinds of masks.

To create a layer clipping mask, place the vector object that will be your mask at the top of the layer’s stacking order. Click once on the layer name in the Layers palette, which selects the layer (you don’t want to target the layer, just select it in the palette). Then, click the Make/Release Clipping Mask icon at the bottom of the Layers palette. The topmost object in your layer now becomes a mask for all objects in that layer. The mask appears listed in the Layers palette with an underline, giving you a visual indication of its behavior. With layer clipping masks, you can easily drag items into a masked layer to have them affected by the mask, and vice versa. To release a layer clipping mask, select the layer and click the Make/Release Clipping Mask button.