Initiatives certifying that farms and firms adhere to predefined environmental and social welfare production standards are increasingly popular. According to proponents, they create financial incentives for farms and firms to improve their environmental and socioeconomic performance. This paper reviews the evidence on whether sustainable certification of agricultural commodities and tourism operations actually has such benefits. It identifies empirical ex post farm-level studies of certification, classifies them on the basis of whether they use methods likely to generate credible results, summarizes their findings, and considers the implications for future research. We conclude that empirical evidence that sustainable certification has significant benefits is limited. We identify just 37 relevant studies, only 14 of which use methods likely to generate credible results. Of these 14 studies, only 6 find that certification has environmental or socioeconomic benefits. This evidence can be expanded by incorporating rigorous, independent evaluation into the design and implementation of projects promoting sustainable certification.