National and international taxes may be used as a means of controlling atmospheric trace gases (ATGs), the principal one of which is carbon dioxide. One can think of such a tax as a “price” for the right to emit ATGs into a global environmental sink. Once the price is fixed, emissions are adjusted and the task before the regulatory authority is to set the right tax, or price, so that the desired level of emissions is obtained. However, the problem can be approached in another way. The regulators could specify the emissions reductions and then allow the market mechanism to determine the price. It would work through the issuance of ATG permits, which would be traded, perhaps on some kind of exchange, and from which a price would emerge. This price would be the equivalent of a tax.