This chapter introduces Actor-Network Theory, a sociotechnical approach to studying health information technology implementation. The chapter is intended as a pragmatic introduction to the field, acknowledging that there are many contested features of an Actor-Network Theory informed methodology. Nevertheless, the approach can be usefully drawn on to help to focus data collection and sampling. A case study describing the application of Actor-Network Theory to study the “failed” implementation of national electronic health records in England as part of a national “top-down” implementation program illustrates the main tenets of the approach and provides concrete examples of how Actor-Network Theory may be applied. In doing so, this chapter offers a reflexive account of how Actor-Network Theory has provided a nuanced analysis of how the implementation of national electronic health records affected different stakeholders, organizations and technology.