We investigate how members of different organizational cultures bring these together to successfully address a shared goal over time. Using extensive observational, interview and archival data collected with TRANSFORM, a joint initiative between Unilever, the UK’s FCDO and EY that supports social enterprises in low-income countries, we find that actors from all three organizations gain cultural fluency, the ability to understand, work with and articulate the cultures of the other organizations. We also find that the joint initiative over time accumulates cultural material tailored to the specific tasks of the initiative and the contexts in which it works through a process of culture formation. Finally, we observe how cultural fluency and culture formation jointly allow for the emergence and maintenance over time of an inter-organizational culture that serves to accomplish the distinct work of the joint initiative while maintaining effective connection to the three parental cultures. Based on our findings, we develop the concept of a bounded, incrementally assembled and dynamically updated inter-organizational culture which informs our understanding of organizational action on problems spanning individual organizations. We theorize cultural fluency, through which actors can navigate the occurrence of frictions or slippages when different cultures come together. Finally, we show how culture interacts with multiple, complex social and natural systems and can (and has to) be matched to different local and global ‘realities’.