In this methods case, I describe why concept development research is relevant in a scientific discipline with focus on caring science. The phenomenon and concept of rest belong to the domain of caring because people need rest to recover from strain and illness to maintain health. If a concept is poorly described in a discipline, it can be developed from qualitative studies and from people's lived experiences of the phenomenon. I describe how phenomenological interviews can be performed in the process of concept development and give some examples from my own experiences. The interviews’ methodological approach is based on lifeworld theory and ideas of the lived body. Also, the epistemological theory about intentionality is a guiding star for data collection and analysis. The lifeworld perspective is in line with ontological assumptions in caring science, where the human being is regarded as an entity of body, mind, and spirit that influences and is influenced by the world. Accordingly, in this research, the assumptions on ontological, epistemological, and methodological levels are consistent.