This thesis investigates the relationship between corporate social performance (CSP) and financial performance. It is motivated by the issues as to whether firms should invest in CSP and how investors value socially responsible companies. This study makes the distinction between financial performance as perceived by the firm, and as perceived by its investors. Consequently, this study examines two research questions. First, this study examines how CSP is associated with corporate financial performance. Second, the association between CSP and expected market return is investigated. The prior research has employed a range of research designs, and has provided evidence suggesting that positive, negative and no associations exist. This study uses the Dow Jones Sustainability Index (DJSI) to identify leading CSP firms, and employs a matched pairs design to compare leading CSP and conventional firms. By conducting univariate and regression tests, the results indicate that leading CSP firms have greater corporate financial performance than conventional firms. Further, the results show that the expected market returns for leading CSP and conventional firms are equivalent. Therefore, the implication from this study suggests that CSP investment leads to greater corporate financial performance. In addition, the results imply that investors suffer no financial trade-off for investing in socially responsible companies.