Fragmented governance of international value chains, operating in multiple jurisdictions, is insufficient to prevent social and environmental mismanagement. Smart Mixes, which are combinations of compulsory and voluntary measures, have been proposed as a possible means of securing environmental and social standards, but the concept has not been operationalised in the academic literature. We aim to identify the factors that have contributed to, or hindered, the success of existing Smart Mixes in three international value chains (conflict minerals, palm oil, and bonds) using data from interviews with thirty two experts, supplemented by a literature review. The results suggest that Smart Mixes are effective when they cover a specific issue under conditions in which enforcement mechanisms create a level playing field: thereby aligning public and private sector interests. The keys to success in a Smart Mix include positive interactions, harmonisation, and complementary and supportive measures, which combine to motivate engagement by the private sector. We conclude that Smart Mixes can contribute to sustainability in value chains but their effectiveness is dependent on the strength of the relationships between the measures that compose them.