This chapter shows that much of our thinking around the ethics of emerging technologies started from very concrete technical practices, in medicine, engineering, and computer science. It follows the stories of three famous practitioners in the history of science and engineering, Hippocrates, Oppenheimer, and Wiener, to explain how ethics emerged in their thinking as a response to the dilemmas they faced in practice. Out of these endeavors, to which countless practitioners have in fact contributed, important ethical frameworks and tools emerged: ethical oaths, regulatory limits to innovation, and ethical impact assessment.