We base our inferences on a sample of firms in 21 countries that adopted IAS between 1994 and 2003. Ideally, we would base our inferences on a sample of firms that are randomly assigned to apply IAS. However, our sample period precedes the mandatory application of IAS for most sample firms, and thus firms may have adopted IAS in response to changed incentives. Thus, we could detect an improvement in accounting quality for firms that apply IAS that is attributable to changes in incentives and not to changes in the financial reporting system. To mitigate the effects of changes in incentives, when constructing our accounting quality metrics relating to earnings management and timely loss recognition, we include controls for factors that prior research identifies as associated widi firms’ voluntary' accounting decisions, for example, growth, leverage, and the need to access the capital markets. Our metrics of accounting quality also reflect die effects of the economic environment that are not attributable to tite financial reporting system. The economic environment includes volatility of economic activity and the information environment. To mitigate these effects, we use a matched sample design by selecting a firm that applies domestic standards in the same country as, and of size similar to, each sample firm that applies IAS. We compare accounting quality metrics for the two groups of firms. In addition, some of the controls we include when constructing our metrics also are proxies for the economic environment. Although we include these research design features, we cannot be sure that our findings are attributable to the change in the financial reporting system rather than to changes in firms’ incentives and the economic environment.