The number of sustainability standards and certifications applied in agricultural supply chains has grown considerably in the past decade, creating confusion for consumers and challenges for producers, particularly small-scale producers in developing countries. This chapter provides an overview of the range of sustainability standards that have emerged, who has developed them, their content and rationale. It also explores how companies select the standards they use, and how this is changing. Recent choices made by brands and retailers accentuate some of the challenges associated with standards for smallholders and further contextualises the mixed picture concerning impacts on smallholders. The chapter provides a summary of implications of sustainability standards, including how they may contribute to improved practices, but highlights limitations of standards on their own as a tool to hold business to account, stressing the importance the overall sustainability strategy of the company, and its commitment to sustainability.