At the candy shop as a child, your fingers on the counter's edge, you peer up at the big jars of candy, filled with sweets. You place your quarter firmly on the counter, and the kind owner nods—you choose exactly one candy from each jar and are soon proudly carrying your treats out of the shop in a crisp white bag. In mathematics, one often finds oneself in just such a situation, with a collection of nonempty sets and an urgent desire, for some mathematical purpose, to select a single item from each set in the family. Is it always possible? Can we always choose a mathematical sweet from each set? Perhaps it seems obvious—just pick an element arbitrarily, randomly choosing an item from each set. Can we expect to choose like the kid in the candy shop?