No dice are fair because you cannot manufacture them with absolute geometrical precision. The closest we can come are D6 casino dice whose manufacture is controlled by Federal and state gaming laws. They are machined to within a few ten thousandths of an inch and the material of the pips (spots) has the same density as the body of the dice. In contrast, D20s are especially problematic, because it is difficult to precisely manufacture a perfect icosahedron. For this reason, we have focused on D20s. Though all dice are unfair, some are very close to fair, and some are not. Using tens of thousands of physical dice rolls, and billions of simulated dice rolls, we have studied several statistical methods for testing dice with special attention on the power of the test. We will also show you a dice mechanic that rolls fair even with unfair dice.