Despite a substantial unfolding investment in Grid technologies (for the development of cyberinfrastructures or e-science), little is known about how, why and by whom these new technologies are being adopted or will be taken up. This chapter argues for the importance of addressing these questions from an STS (science and technology studies) perspective, which develops and maintains a working scepticism with respect to the claims and attributions of scientific and technical capacity. We identify three interconnected topics with particular salience for Grid technologies: data, networks, and accountability. The chapter provides an illustration of howthese topics might be approached from an STS perspective, by revisiting the idea of “virtual witnessing”—a key idea in understanding the early emergence of criteria of adequacy in experiments and demonstrations at the birth of modern science—and by drawing upon preliminary interviews with prospective scientist users of Grid technologies. The chapter concludes that, against the temptation to represent the effects of new technologies on the growth of scientific knowledge as straightforward and determinate, e-scientists are immersed in structures of interlocking accountabilities which leave the effects uncertain.