The study examined how science faculty who teach introductory science courses including the fields of chemistry, biology, physics, and earth science, understand and define science and nature of science (NOS), how these instructors teach the aspects of NOS to their students, and the rationales they provide for their teaching practices. Participants were seventeen science instructors from five different institutions in the northeastern U.S. Participants were interviewed and four of them were further observed in their settings. Consistent with previous research, the findings revealed that the participants held sophisticated and complex conceptions of NOS. In some instances their views were in line with the views promoted by science philosophers, and in other instances their views were more mixed and naive. Results suggest reducing the size of classes to allow for more meaningful instruction. The examples, quotations, and results from this study may be useful for teacher educators and sciene faculty. However, the intent of this research is not to provide generalizations to all scientists who teach introductory science. Such claims would extend beyond the scope of the research design.