In theory, software, like other digital artifacts, can be freely copied and distributed. In practice, however, its effective flow is conditioned on various technical and social factors. In this paper, drawing on ethnographic work primarily with a bio-informatics research team in China, we report on meanings of scientific software sharing as embedded in social practices of learning, apprenticeship, membership, publication, and reputation. We illustrate that while free flow is important, boundary management is equally important for the effective travel of software to its appropriate destinations. Our study highlights a number of issues that are important to consider for effectively supporting sharing and collaboration in science.