SA 8000, along with other types of certification standards and corporate codes of conduct, represents a new form of private governance of working conditions, initiated and implemented by companies, labor unions, and non-governmental activist groups. Whether these codes represents a substantive or merely symbolic approach to governing working conditions is the subject of an ongoing debate, which to date has been dominated by philosophical and political discourse due to a lack of systematic evaluation. Very little empirical evidence is available to indicate whether these codes legitimately distinguish adopting companies and factories as providing better working environments (e.g., health and safety, freedom of association, fair pay practices) and whether these codes have affected their business outcomes (e.g., staff turnover and absenteeism, product defect rates, sales growth). In this book chapter, we review the existing evaluations of other private codes governing workplace conditions, including the Ethical Trading Initiative's Base Code, Nike's code of conduct, and Fair Trade. We then describe several key elements of program evaluation that are becoming standard practice in other domains, which we believe should be incorporated in future evaluation studies of these codes. We emphasize the importance of examining performance over time, comparing adopters to non-adopters, and incorporating strategies to overcome selection bias. Evaluations that meet the highest methodological standards are critical to inform the debates about this new form of private governance, and to highlight opportunities for improvement in their standards and monitoring procedures.