One of the cornerstones of organic farming is the fact that it is governed by clear standards which are legally protected in many parts of the world, but there is concern that the current certification system does not fully safeguard the objectives and principles of the movement and encourage further improvements in sustainability. The chapter provides a brief history of organic standard development, and introduces the values and principles of organic farming that have guided this process. The chapter discusses advantages and disadvantages of the different types of rules currently used to achieve common objectives, such as prohibitions or obligations to use specified inputs and practices. The chapter explores whether trends in sustainability assessment could help to close the gap between ambition and rules, concluding that research can improve the evidence base, evaluate the impact of standards and produce a better understanding of the barriers that prevent new producers from converting to organic farming.