The article ties together codified ethical premises, proceedings of ethical reasoning, and field-specific ethical reflections so to inform the ethnography of an Internet-based collaborative project. It argues that instead of only obeying formal statutes, practical judgment has to account for multiple understandings of ethical issues in the research field as well as for the self-determination of reflexive participants. The article reflects on the heuristics that guided the decisions of a 4-year participant observation in the English-language and German-language editions of Wikipedia. (...) Employing a microsociological perspective, it interrogates the technological, social, and legal implications of publicness and information sensitivity as core ethical concerns among Wikipedia authors. The first problem area of managing accessibility and anonymity contrasts the handling of the technologically available records of activities, disclosures of personal information, and the legal obligations to credit authorship with the authors’ right to work anonymously and the need to shield their identity. The second area confronts the contingent addressability of editors with the demand to assure and maintain informed consent. Taking into account these problem areas, the ethical reasoning on the one hand proposes options for observing and documenting episodes. On the other, it provides advice on the feasibility and the necessity of obtaining informed consent. (shrink)