When is a game only a game? To date, articles on the taxation of activities in virtual worlds have not attempted an answer to this question. Instead, they have attempted to formulate rules applicable equally to worlds created solely for entertainment purposes and worlds structured to serve as venues for serious economic activity. This article proposes a bright-line test, at least with respect to the taxation of cash method taxpayers, for distinguishing between these two types of worlds. Transactions in worlds whose currencies are redeemable or convertible, it argues, should be subject to current taxation under standard cash method timing rules, applied in-world. Transactions in worlds whose currencies are neither redeemable nor convertible, by contrast, should not be currently taxable. Activities in such worlds should be treated, rather, as non-taxable entertainment unless and until players engage in real money trades. Although articulated in the context of virtual worlds, the proposed test works equally well in distinguishing taxable from non-taxable real-world games. Pinball points are neither redeemable nor convertible. If an accumulation of pinball points results in further game play, the proposed test suggests that the winning of such further game play should not be taxable. Casino chips, by contrast, are redeemable. The receipt of casino chips as gaming winnings should therefore be treated as an immediately taxable event; we should not have to wait until the patron cashes out to tax her winnings. In the course of its analysis, the Article offers, in addition, a new take on the concept of realization and a new formulation of the cash equivalence doctrine.