Information systems can only reach their full potential if their implementation is effective, and there is much to be learned as to what makes an “effective” implementation. In light of the substantial investments in Health Information Technology internationally, implementation evaluations are a powerful tool to ensure that technologies are enabled to fulfil their potential in improving care, reducing cost and increasing efficiency. The most salient characteristics of such evaluations are outlined, considering how they can help to assess adoption processes and outcomes through a continuous cycle of scientific enquiry and learning. A brief description surrounding potential theoretical lenses that may be drawn on is given. Issues discussed will be illustrated with the help of a case study on the implementation and adoption of Electronic Health Records in English hospitals. Practical challenges encountered and potential ways to address these during the conduct of health IT implementation evaluations illustrated include: 1) ways to cope with the shifting nature of reality (e.g. changes in local implementation strategies need to be reflected in the methods), 2) the need to examine processes as well as outcomes, 3) researching implementation in context with attention to both local processes and wider (e.g. political) developments, and 4) the pragmatic use of theoretical lenses where different approaches can shed light on different aspects of the implementation and adoption process.