1 Guest editorial Knowledge infrastructures: Part II Helena Karasti Department of People and Technology, Roskilde University, Denmark / hkarasti@ruc.dk Information Systems, Luleå University of Technology, Sweden / helena.karasti@ltu.se INTERACT, University of Oulu, Finland / helena.karasti@oulu.fi Florence Millerand Department of Public and Social Communication, University of Quebec at Montreal, Canada / millerand.florence@uqam.ca Christine M. Hine Department of Sociology, University of Surrey, UK / c.hine@surrey.ac.uk Geoffrey C. Bowker Department of Informatics, University of Irvine, CA, USA / gbowker@uci.edu The papers presented here were submitted in response to a call for papers that sought to draw together the current state of understanding of knowledge infrastructures from the viewpoint of STS and to provide a basis from which to evaluate the distinctive contribution that the theoretical resources of STS were making within this territory. That call for papers produced a high level of response, providing a clear indication that STS scholars are indeed taking knowledge infrastructures seriously, and that the study of infrastructures is providing fruitful ground for developing insights into STS’s core concerns with interrogating the complex, emergent sociotechnical systems that pervade the contemporary world. The initial call for papers produced more successful submissions than could be accommodated in a single issue of the journal, and hence the envisaged special issue will, in fact, extend across multiple issues of which this is the second. In the previous issue of Science & Technology Studies, we presented an initial batch of three substantively very different studies: Wyatt et al. (2016) explored the treatment of controversy within the production of the Wikipedia entry relating to schizophrenia genetics; Parmiggiani and Monteiro (2016) examined the production of infrastructures relating to the monitoring of environmental risk in offshore oil and gas operations; and Boyce (2016) analysed the work of connecting infrastructures for public health surveillance. Despite the differing substantive foci we were able to draw out some significant cross-cutting themes. The issue of scale received considerable attention, as the papers each explored what were on the face of it large scale infrastructures but were sustained by contingent connections forged across macro-level visions of possible outcomes and diverse forms of micro-level work developing technologies, connecting systems, generating content, overcoming obstacles and managing breakdowns. Our editorial (Karasti et al., 2016) took a reflexive turn, considering the significance of the methodological choices that underpinned these studies of infrastructures and the intransigence of some aspects of infrastructure in the face of our attempts to comprehend them. We noted that the choice of where and how to study such infrastructures involves