This article explores how the green, sustainable city is built in situations of uncertainty though professional practical engagements of testing and trying, and how these are formed by moral investments in professional work. Following recent studies investigating professional work and moral agency, the article engages with Terence Halliday’s famous distinction between science-based and normative professions. Contrary to this argument, the article argues that the practice of engineers, the clearest example of the so-called ‘science-based’ profession, is fraught with moral questions and practices. By drawing on French pragmatic sociology, the article conceptualizes the different ways engineers and others work in situations of uncertainty as different modes of trying. In these modes, professionals rely on different moral principles and ideas for evaluating and judging the professional solutions. As such, the article contributes to the sociology of professions by suggesting a new analytical frame for analyzing moral work as fundamental to professional practice in situations of uncertainty. Empirically, the article builds on fieldwork observations and interviews with professionals from an ongoing research project on Danish climate adaptation in cities and urban rainwater management.