There is growing consensus around the limited attention given to documenting the process of intervention development, specifically the role of qualitative research. In this article, we seek to describe a missing piece of this process: how qualitative research, and related methodologies and theories, informs intervention development. We use our research as a case study of “reflexive intervention development.” We begin by describing our interview study, consisting of 23 in-depth interviews with women diagnosed with metastatic breast cancer, and go on to detail our methodological framework and research team. We then explain how this interview study directly informed our development of the intervention materials, allowing us to attend carefully to language and its potential implications for women. We conclude by inviting researchers to reflect on the knowledge production process that is inherent in intervention development to consider not only their role in this process but also the role of qualitative research.