Writing reflects some of the different characteristics of the language being used and of the people who are communicating. The present paper focusses on the internal written communication in international and inter-disciplinary research projects. Using a case study of an international public health research project, it argues that the authorship and the languages used in internal project communication are not neutral but help to generate or reinforce power hierarchies. Within research partnerships, language thus raises ethical issues that have so far been neglected. Current ethics guidelines often focus on interactions between scientists and participants of social research and clinical trials, with less attention paid to the interactions among the scientists themselves. Describing all the different project phases based on writing within a research project, the paper distinguishes different influences on the distribution of power that emerge through a focus on written communication. The focus of the present paper is to illuminate the issues of ethics, power and the dimensions of hierarchy, physical location and native versus non-native English speakers that arise from paying attention to such communications.