Healthcare professionals frequently feature on the news and in history as witnesses to difficult events: genocide, war crimes, disasters and catastrophes. Their accounts often have a major impact on how such events are perceived and understood. In this knowledge synthesis, we will consider what roles testimonies by healthcare professionals play in evolving narratives linked to four specific case studies: the Holocaust, the Union Carbide Gas Leak Disaster in Bhopal (1984), the 2010 Haiti earthquake and the climate crisis. Through analysing data linked to the case studies, we will address to what extent existing research examines both the important function testimonies by medical practitioners have played in enhancing knowledge and understanding of such catastrophes, how such testimony in times of crisis is now often closely linked with strategic communications by humanitarian organisations and how the emergence of new technologies and online platforms has led to changes in the ways such accounts are produced and received. Healthcare professionals are often called upon to perform the role of what Robert Jay Lifton has called 'witnessing professionals,' tasked with confronting narrative falsehoods and calling out destructive behaviour. How and whether they should bear witness has also been a subject of controversy, as is evident in the well-known different approaches of the Red Cross and Médécins Sans Frontières. Through our data analysis we will ascertain whether the qualitative differences that characterize their testimonies as forms of knowing in comparison with accounts by other potential witnesses has been adequately examined. Equally, we will consider what the data reveals (or fails to) about the varied ways such testimonies are shaped by strategic communication challenges and how they are received by a non-medical professional audience. Our project will also analyse what data exists regarding the question of technological innovation and its effects on the production and dissemination of witness accounts by healthcare workers. Through the knowledge synthesis we will produce, we will generate an invaluable overview of the current state of research regarding the crucial roles witnessing by healthcare professionals perform in shaping knowledge. The research will have considerable value to doctors and nurses working for organizations such as aid agencies who may regularly confront, and need to attest to, the effects of conflicts and disasters. It will also be of interest to the communications teams of humanitarian aid organizations, potentially helping to refine their communications policies, helping to gauge effectiveness and identify areas for improvement. The scoping review will also provide an important resource for researchers and teachers. Better comprehension of what impacts the form and effectiveness of testimony will help healthcare professionals who are called upon to provide it to deliver their accounts as effectively as possible. The synthesis will also pinpoint areas in which narratives are at risk of exclusion or marginalization because healthcare traditions differ from the dominant biomedical paradigm. Traditional healers, for instance, can offer important testimony to the impact of climate change (including damage to the environment that bears upon the availability of medicinal plants, for example) yet risk not being heard as they are not viewed as 'professional'. Enhanced knowledge about potential exclusions and a lack of diversity will have considerable value for media organizations seeking balance in their coverage of conflict and disasters. Additionally, having a greater understanding of the extent and limitations of current research in the area will lay the groundwork for more focussed and effective studies moving forward. Such studies will potentially have major policy implications relating to local or international crisis responses.