ABSTRACT:We describe a longitudinal study of a secondary education biology teacher at two moments in her career (1993 -2002), determining the changes in her conceptions of the nature of science and its teaching and learning, and the factors that favored or hindered such changes. The changes were analyzed using cognitive maps, constructed on the basis of the Inventory of Teachers' Pedagogical & Scientific Beliefs (INPECIP) questionnaire, designed and validated by R. Porlán, A. Rivero, and R. Martín del Pozo (1997), and a semistructured interview. The results showed the process of change in conceptions to be complex and gradual, with different conceptions being out of phase with each other. During her first 4 years of teaching, until 1993, her conceptions of science teaching and learning began to evolve from a teacher and content-centered model to one that was more student