This article explores the divergent and diverging approach to sustainability agreements in the EU, UK and US, and the practical impact of this on businesses. After considering the underlying debate around the role of competition policy in relation to sustainability, it analyses the written sustainability guidelines and informal guidance policies adopted by the European Commission and the Competition and Markets Authority (highlighting key similarities and differences), before setting out the contrasting approach taken by the antitrust authorities in the US. This article concludes by focusing on the practical impact of this divergence on businesses and providing the authors’ thoughts on where to go from here.