Carbon emissions emanating from infrastructure construction are substantial, and public infrastructure clients have begun to include carbon reduction goals in their procurement requirements. This is a new and complex field where practices vary and are still developing. Based on project documentation and interviews we map and analyze the design and implementation of carbon reduction requirements in projects by leading infrastructure clients in Australia, the Netherlands, Sweden, the US and the UK. Procurement requirements were influenced by concerns for tender competition, transaction costs and innovation, and further adapted to project delivery models, market maturity and client capabilities. Increasing awareness of practical and contextual constraints often led to modified strategies. This paper identifies factors that should be considered when designing carbon policies and requirements. This knowledge is important for clients and governments in order to develop more effective strategies for learning between contexts. Policies and future research should address client capabilities to drive long-term innovation.