Aquantum dot, as its name implies, is a minuscule region of metallic or semiconductor material whose dimensions can be as small as a few tens of nanometers on a side. It has been likened to an artificial atom because it carries a discrete charge and quantized electronic energy levels (see the article by Marc Kastner in PHYSICSTODAY, January 1993, page 24). That analogy has now been taken a step further with the demonstration that a quantum dot interacts with nearby metallic leads in much the same way that a single magnetic impurity interacts with a surrounding metallic substance—in the phenomenon known as the Kondo effect.