Transaction costs are omnipresent in markets yet are often omitted in economic models. We show that their presence can fundamentally alter incentives and welfare in markets in which the price equates supply and demand. We categorize transaction costs into two types. Asymptotically...

Fees are omnipresent in markets but, with few exceptions, are omitted in economic models-such as Double Auctions-of these markets. Allowing for general fee structures, we show that their impact on incentives and efficiency in large Double Auctions hinges on whether the fees are homogeneous (as,...

The annual adverse effects of pollution are on the order of 10% of world GDP. Many approaches are used or have been proposed to control the growing pollution problem, but none of them allows for efficient pollution control in settings in which the marginal cost of pollution is increasing and...