A frother uses a motorized whisk to froth milk, while a steamer uses pressurized steam to heat milk and create smooth microfoam. In most cases, you'll get more foam with a milk frother because the process of frothing introduces air into the milk, which is what makes it so light and foamy. Steamed milk isn't quite as foamy, with a more velvety texture. While the textures are slightly different, you probably don't need a separate frother if your espresso machine has a steam wand.