This article explores via the concept of professional jurisdiction how engineers shape and maintain authority in practice, and points to the important role of specific professional documents in this practice. Drawing on the sociology of conventions, the article shows how the documents work as standardized and ‘invested’ forms that help professional actors coordinate internally in the profession, as well as compromise, maintain boundaries and forge alliances with actors outside the profession. Empirically, the article analyses historic documents, called writings, from a professional committee under the Danish Society of Engineers, and shows how these documents have helped engineers shape and maintain authority over the Danish field of urban water management.