HCI scholars have become increasingly interested in describ- ing the complex nature of UX practice. In parallel, HCI and STS scholars have sought to describe the ethical and value- laden relationship between designers and design outcomes. However, little research describes the ethical engagement of UX practitioners as a form of design complexity, including the multiple mediating factors that impact ethical awareness and decision-making. In this paper, we use a practice-led approach to describe ethical complexity, presenting three varied cases of UX practitioners based on in situ observations and interviews. In each case, we describe salient factors relat- ing to ethical mediation, including organizational practices, self-driven ethical principles, and unique characteristics of specific projects the practitioner is engaged in. Using the concept of mediation from activity theory, we provide a rich account of practitioners’ ethical decision making. We pro- pose future work on ethical awareness and design education based on the concept of ethical mediation.