The pedagogic practical knowledge that teachers use in their lessons is very difficult to make visible and often remains tacit. This chapter draws on data from a recent study and closely analyses a number of Open Educational Resources used by three language teachers at the UK Open University in order to try to capture how their use of the resources is informed by their cognitive, affective and systemic tacit professional knowledge. The chapter concludes that Open Educational Resources and practices can enable us to transform tacit knowledge into shared, commonly usable knowledge, which might result in better learning experiences and practices. [For the complete book, "10 Years of the LLAS eLearning Symposium: Case Studies in Good Practice", see ED577046.]