Knowledge translation is the process of taking evidence from research and applying it in clinical practice. In this article I will cite some pivotal moments in the history of medicine to highlight the difficulties and delays associated with getting evidence into practice. These historical examples have much in common with modern medical trials and quality improvement processes. I will also review the reasons why evidence is not used and consider what factors facilitate the uptake of evidence. Understanding these concepts will make it easier for individual clinicians and institutions to change clinical behaviour and provide a starting point for those looking at implementing 'new' practices, new therapies and clinical guidelines. Finally, I will offer a list of criteria that clinicians might choose to consider when deciding on whether or not to adopt a new practice, treatment or concept.