The typical economic model implicitly assumes that the set of goods in an economy never changes. As a result, the predicted efficiency loss from a tariff is small, on the order of the square of the tariff rate. If we loosen this assumption and assume that international trade can bring new goods...

From the beginning, growth theory has been faced with technically challenging questions about increasing returns and the way to capture ideas in a model of market exchange. Initially, reliance on perfect competition forced growth theory to narrow its scope. Recently, new tools for studying...