Hundreds of “eco-labels” and “social labels” exist for consumer products. These labels claim to provide information about characteristics of these products, which consumers cannot directly observe but which many of them consider desirable, such as low environmental impact, good treatment of workers during production, and relatively high prices paid to the local producers of ingredients from developing countries. Third-party certifiers are supposed to solve the well-known problem that a producer's unilateral declarations lack credibility, given the producer's conflict of interest and the information asymmetries between producer and consumer. Much of the literature on global private regulation—through standards for environmental sustainability, corporate social responsibility, among others—assumes that third-party certification works (i.e., overcomes the problems of producer self-declaration). But closer inspection shows that many third-party certifiers lack credibility. This article examines why some third party certifiers are more credible than others. In doing so, we elucidate the ways in which social capital and trust bolster third party certifiers' credibility. The empirical analysis focuses primarily on Kosher food labels within the global food supply chain. We then explore the consequences of the credibility paradox for other third party certified labels that promote social and environmental values.