This research focuses on inservice science teachers' conceptions of nature of science (NOS) before and after a two-week intensive summer professional development (PD). The PD combined traditional explicit NOS instruction, numerous interactive interventions that highlighted NOS aspects, along with documentary films that portrayed NOS in context of authentic scientific discovery. Reflective dialogue was used throughout the professional development to encourage constructivist learning. The PD addressed seven commonly held NOS tenets that are deemed significant to K-12 science teachers. Finally, qualitative methodologies were used to analyze the Views of Nature of Science Questionnaire (VNOS-D) and the associated interview data to explore subtleties within each NOS tenet and to gain a richer understanding of how the teachers' NOS understanding differed before and after the PD.