This thesis presents the findings from an ethnography of stem cell science based on fieldwork with researchers in two connected laboratories in Scotland and the United States. It explores stem cell scientists' complicated interactions with live stem cell cultures within national projects of translational regenerative medicine. This analysis both draws upon and contributes to the social studies of biomedicine, reproductive studies and science and technology studies. I examine how stem cell scientists, involved in an international research initiative, navigate the challenging landscapes of translational regenerative medicine and attempt to transform fragile live cell cultures into successful biotechnical, medical and economic products. By considering translational regenerative medicine as an effort to reformulate the relationship between biology and technology in terms of applicability and utility, I illuminate tensions between the specific practices of care that enable stem cell growth in vitro and the elusive goals of national projects of biotechnological innovation. A major focus of this study is the means by which scientists in the two laboratories manage the inherent uncertainties of both cell culture and translational science. By exploring how researchers react to unstable and unpredictable cellular behaviour in the laboratory, while also managing the expectations of government and external funding bodies, I provide a portrait of the complex sociality of contemporary bioscience. In addition to the international collaboration between the two laboratories, I explore scientists' interdisciplinary work with medical specialists and public engagement with stakeholders in regenerative medicine. In doing so, I pay attention to the ways in which scientists themselves deal with and reflect on the relational and interdependent nature of their endeavours. Drawing on twenty-two months of ethnographic fieldwork and fifty qualitative interviews, I show how stem cell scientists' new engagement practices also inform scientific work and the care of stem cells in the laboratory. In short, I argue that translation of science across different sites at once creates and depends on new social relations between stem cells, people and communities. After providing an overview of the literature, central questions and methodology that frame this thesis, I introduce the opportunities and challenges that translational regenerative medicine goals create for the care of stem cells in vitro. From there, I zoom out beyond the tissue culture flask to demonstrate how the necessity for science applicability creates new responsibilities for scientists to connect with stakeholders in regenerative medicine outside of the laboratory. I conclude that a consideration of scientists' ties and societal links is significant for an understanding of the connection between the biological and the technological.