This paper describes the process of investigating a teacher's knowledge and pedagogical philosophy through using a biographical rendition of a teacher's knowledge grounded in a construction of present teaching practice, based on ethnographic data. A case study is presented demonstrating how a major component of one teacher's present knowledge of her practice, the "idea of responsibility", has changed throughout her career. A discussion is presented illustrating how a grounded conceptualization of this teacher's present pedagogy emerged from an ethnographic approach to her actions in the classroom. Following a description of what the "idea of responsibility" means in terms of her current teaching practices, its various manifestations at different moments in the teacher's life are examined, as well as how transformations occurred in the teacher's thinking. Some issues concerning the potential of combined ethographic and biographical approaches to the study of teacher's knowledge as a process are raised. In Part One of the paper, an outline is given of the ethnographic study, how data were collected and interpreted, and the progressive stages of the ethnographic investigation. A discussion is offered on her philosophy of teaching, approach to children, conception of learning and subject matters, and curriculum materials, and how she transforms theory into practice. In Part Two, the collection of biographical data and their interpretation is discussed. Concluding comments offer reflections on the validity of combining ethographic and biographical approaches in the study of the formation of a teacher's pedagogy. (JD)