Sustainability of food production has become the focus of many research projects and has gained a prominent position in the marketing of food products. To gain insight into the sustainability performance of farms, and ultimately support farmers in sustainable development, a large number of sustainability assessment tools have been developed. This expectation has made sustainability assessment tools increasingly popular to measure sustainability. The actual implementation of assessment tools in practice, and contribution of assessments to change, however, is being questioned. In fact, the movement towards 'better' sustainability assessment tools is being caught between two conflicting trends: the continual proliferation of sustainability assessment tools and the streamlining of market assurance programmes that give the impression of certainty in assessing sustain ability. In this viewpoint article, we identify current limitations of sustainability assessments to catalyse change and formulate recommendations to the developers and users of such tools. We argue that challenges of implementation are, in part, related to the ambition of the assessment and their associated level of comprehensiveness. As a sustainability assessment becomes more comprehensive, and covers a wider range of issues or practices, the difficulty of implementing the sustainability assessment increases. We also highlight that the implementation challenge can be connected to the credibility, salience and legitimacy of knowledge produced by sustainability assessments. We conclude that increasing the transparency, harmonization, participation and sensitivity to farmer' motivation in sustainability assessments is urgently needed to better link sustainability knowledge to action and overcome the current lock-in.