This paper provides new empirical evidence for the effect of corporate social responsibility (CSR) on corporate financial performance. In contrast to former studies, we examine two different regions, namely the USA and Europe. Our econometric analysis shows that envi-ronmental and social activities of a firm compared with other firms within the industry are valued by financial markets in both regions. However, the respective positive effects on av-erage monthly stock returns between 2003 and 2006 appear to be more robust in the USA and, in addition, to be nonlinear. Our analysis furthermore points to biased parameter esti-mations if incorrectly specified econometric models are applied: The seemingly significantly negative effect of environmental and social performance of the industry to which a firm be-longs vanishes if the explanation of stock performance is based on the Fama-French three-factor or the Carhart four-factor models instead of the simple Capital Asset Pricing Model.